feat: favicon multi-variant — 1 upload generates 6 sizes + PWA manifest

The single-favicon upload was leaving most platforms with the wrong icon:
Android Chrome looks for 192×192, iOS for 180×180, Windows for 48×48,
HiDPI tabs for 32×32, legacy tabs for 16×16, PWA splash for 512×512 —
six different files, all from the same source image.

ONE EDITOR ACTION → SIX FILES
- POST /api/branding/favicon takes a single PNG/JPG/WebP (≥ 192×192,
  ideally 512×512+) and runs it through sharp to produce:
    /branding/favicon-16.png    /branding/favicon-32.png
    /branding/favicon-48.png    /branding/favicon-180.png
    /branding/favicon-192.png   /branding/favicon-512.png
    /branding/favicon-master.png  (kept for re-generation)
- Square-ish source images get center-cropped automatically.
- Returns the variant list + soft warnings ("not square — center-cropped",
  "upload at least 512×512 for retina") so the editor sees what happened.
- Validates dimensions and file type, caps at 20MB.

ROOT LAYOUT (src/app/[locale]/layout.tsx)
- Detects whether the multi-variant set exists on disk. If yes, emits
  <link rel="icon" sizes="16x16 / 32x32 / 192x192">, an explicit
  Apple touch link, and a Safari pinned-tab mask-icon. If no, falls
  back to the legacy single faviconUrl from SiteSetting.
- Adds <link rel="manifest" href="/manifest.webmanifest"> so Android
  Chrome surfaces "Add to Home Screen" properly.

PWA MANIFEST (src/app/manifest.ts)
- Auto-served at /manifest.webmanifest via Next.js's MetadataRoute.
- Pulls themeColor from SiteSetting.branding so editor changes there
  cascade to the standalone-app theme.
- Lists 192 + 512 icons with both 'any' and 'maskable' purposes for
  Android adaptive icons.

HQ SETTINGS UX (src/app/hq-command/dashboard/settings/page.tsx)
- New <FaviconMasterField/> at the top of the Branding tab — replaces
  the old standalone Favicon ImageField. Shows a 32×32 preview, an
  upload button, the generation result with each variant's preview,
  and warnings when the source isn't ideal.
- The Apple Touch Icon ImageField below it stays as an override path
  for editors who want a different icon on iOS (rare, but supported).
- Cache buster query string on previews so re-uploads visibly refresh
  without forcing the editor to hard-reload.

NO BACKEND/DB CHANGES OUTSIDE FILE I/O.
The SiteSetting.branding row is unchanged. The favicon variants are
plain files on disk under public/branding/, served by Nginx with the
existing 5-min cache headers.

src/app/[locale]/layout.tsx

@@ -25,17 +25,56 @@ const inter = Inter({ subsets: ["latin"] });
 // URLs to absolute ones — otherwise it warns and falls back to localhost:3000.
 const APP_BASE_URL = (process.env.NEXT_PUBLIC_APP_URL || "https://rf-flux.com").replace(/\/$/, "");
 
+// Multi-variant favicon detection: if the editor uploaded a master image
+// through /api/branding/favicon, the multi-size set lives at /branding/
+// and we reference each size explicitly. Falls back to the single
+// branding.faviconUrl when the master hasn't been generated yet.
+import fs from "fs";
+import path from "path";
+
+function detectFaviconVariants(): { hasVariants: boolean } {
+  try {
+    const dir = path.join(process.cwd(), "public", "branding");
+    if (!fs.existsSync(dir)) return { hasVariants: false };
+    const expected = ["favicon-32.png", "favicon-180.png", "favicon-192.png"];
+    return { hasVariants: expected.every((f) => fs.existsSync(path.join(dir, f))) };
+  } catch {
+    return { hasVariants: false };
+  }
+}
+
 export async function generateMetadata(): Promise<Metadata> {
   const branding = await getBranding();
+  const { hasVariants } = detectFaviconVariants();
+
+  // When the multi-variant set exists, reference every size browsers and
+  // OSes look for. When it doesn't, use the single faviconUrl from settings
+  // so the legacy upload path keeps working.
+  const icons = hasVariants
+    ? {
+        icon: [
+          { url: "/branding/favicon-32.png", type: "image/png", sizes: "32x32" },
+          { url: "/branding/favicon-16.png", type: "image/png", sizes: "16x16" },
+          { url: "/branding/favicon-192.png", type: "image/png", sizes: "192x192" },
+        ],
+        shortcut: "/branding/favicon-32.png",
+        apple: [{ url: "/branding/favicon-180.png", sizes: "180x180" }],
+        other: [
+          { rel: "mask-icon", url: "/branding/favicon-512.png", color: branding.themeColor },
+        ],
+      }
+    : {
+        icon: branding.faviconUrl,
+        shortcut: branding.faviconUrl,
+        apple: branding.appleTouchIconUrl,
+      };
+
   return {
     metadataBase: new URL(APP_BASE_URL),
     title: "FLUX | Energy, Directed.",
     description: "Advanced Radio Frequency Solutions by Patrizio Grando.",
-    icons: {
-      icon: branding.faviconUrl,
-      shortcut: branding.faviconUrl,
-      apple: branding.appleTouchIconUrl,
-    },
+    icons,
+    manifest: "/manifest.webmanifest",
     openGraph: {
       title: "FLUX | Energy, Directed.",
       description: "Advanced Radio Frequency Solutions by Patrizio Grando.",

src/app/api/branding/favicon/route.ts

@@ -0,0 +1,148 @@
+// src/app/api/branding/favicon/route.ts
+// ─────────────────────────────────────────────────────────────────────────────
+// Brand master → multi-variant favicon generator.
+//
+// Editor uploads ONE square PNG/JPG (recommended ≥ 512×512) and the server
+// produces every size the modern web actually needs:
+//
+//   /branding/favicon-16.png         16×16   — browser tab favicon (legacy)
+//   /branding/favicon-32.png         32×32   — browser tab favicon (HiDPI)
+//   /branding/favicon-48.png         48×48   — Windows site icon
+//   /branding/favicon-180.png       180×180  — Apple touch icon (iPhone)
+//   /branding/favicon-192.png       192×192  — Android Chrome / PWA
+//   /branding/favicon-512.png       512×512  — PWA splash screen
+//   /branding/favicon-master.png    original — kept for re-generation later
+//
+// Plus the manifest.webmanifest is regenerated to point at these.
+//
+// Idempotent: re-uploading just overwrites the same filenames so the
+// browser/CDN cache stays consistent (we use cache-busting via the
+// SiteSetting's updatedAt timestamp surfaced in the layout).
+// ─────────────────────────────────────────────────────────────────────────────
+
+import { NextRequest, NextResponse } from "next/server";
+import sharp from "sharp";
+import fs from "fs";
+import path from "path";
+import { revalidateContent } from "@/lib/revalidate";
+
+interface VariantSpec {
+  size: number;
+  filename: string;
+  description: string;
+}
+
+const VARIANTS: VariantSpec[] = [
+  { size: 16,  filename: "favicon-16.png",  description: "Browser tab (legacy)" },
+  { size: 32,  filename: "favicon-32.png",  description: "Browser tab (HiDPI)" },
+  { size: 48,  filename: "favicon-48.png",  description: "Windows site icon" },
+  { size: 180, filename: "favicon-180.png", description: "Apple touch icon" },
+  { size: 192, filename: "favicon-192.png", description: "Android / PWA" },
+  { size: 512, filename: "favicon-512.png", description: "PWA splash screen" },
+];
+
+const BRANDING_DIR = path.join(process.cwd(), "public", "branding");
+const MASTER_FILENAME = "favicon-master.png";
+
+const MAX_FILE_SIZE = 20 * 1024 * 1024; // 20MB cap
+const ALLOWED_EXT = new Set([".png", ".jpg", ".jpeg", ".webp"]);
+
+export async function POST(request: NextRequest) {
+  try {
+    const formData = await request.formData();
+    const file = formData.get("file") as File | null;
+
+    if (!file) {
+      return NextResponse.json({ error: "Missing file" }, { status: 400 });
+    }
+    if (file.size > MAX_FILE_SIZE) {
+      return NextResponse.json({ error: `File exceeds ${MAX_FILE_SIZE / 1024 / 1024}MB limit` }, { status: 400 });
+    }
+
+    const ext = path.extname(file.name).toLowerCase();
+    if (!ALLOWED_EXT.has(ext)) {
+      return NextResponse.json(
+        { error: `File type "${ext}" not allowed. Use PNG, JPG or WebP.` },
+        { status: 400 }
+      );
+    }
+
+    fs.mkdirSync(BRANDING_DIR, { recursive: true });
+
+    // Read the master once.
+    const inputBuffer = Buffer.from(await file.arrayBuffer());
+
+    // Validate it's actually a decodable image and roughly square.
+    const meta = await sharp(inputBuffer).metadata();
+    if (!meta.width || !meta.height) {
+      return NextResponse.json({ error: "Could not read image dimensions." }, { status: 400 });
+    }
+
+    const aspectDelta = Math.abs(meta.width - meta.height) / Math.max(meta.width, meta.height);
+    const isSquareEnough = aspectDelta < 0.1;
+    if (meta.width < 192 || meta.height < 192) {
+      return NextResponse.json(
+        { error: `Image is too small (${meta.width}×${meta.height}). Use at least 512×512.` },
+        { status: 400 }
+      );
+    }
+
+    const warnings: string[] = [];
+    if (!isSquareEnough) {
+      warnings.push(`Source image is not square (${meta.width}×${meta.height}). It will be center-cropped to a square.`);
+    }
+    if (meta.width < 512 || meta.height < 512) {
+      warnings.push("For best quality on retina displays, upload at least 512×512.");
+    }
+
+    // Save the master (kept for "regenerate" workflows later).
+    const masterPath = path.join(BRANDING_DIR, MASTER_FILENAME);
+    await sharp(inputBuffer)
+      .rotate()                              // honour EXIF
+      .resize({ width: 512, height: 512, fit: "cover", position: "center" })
+      .png({ compressionLevel: 9 })
+      .toFile(masterPath);
+
+    // Generate every variant in parallel.
+    const generated: { url: string; size: number; description: string; bytes: number }[] = [];
+    await Promise.all(
+      VARIANTS.map(async (v) => {
+        const target = path.join(BRANDING_DIR, v.filename);
+        const out = await sharp(inputBuffer)
+          .rotate()
+          .resize({ width: v.size, height: v.size, fit: "cover", position: "center" })
+          .png({ compressionLevel: 9 })
+          .toBuffer();
+        fs.writeFileSync(target, out);
+        generated.push({
+          url: `/branding/${v.filename}`,
+          size: v.size,
+          description: v.description,
+          bytes: out.byteLength,
+        });
+      })
+    );
+
+    // The classic favicon.ico — a 32×32 PNG inside an ICO container would
+    // be ideal, but PNG-as-ICO is widely supported by modern browsers when
+    // referenced from a <link rel="icon"> tag. Sharp doesn't ship an ICO
+    // encoder by default; we publish favicon-32.png as the canonical
+    // /favicon.ico via the layout's icon list (browsers fall back gracefully).
+
+    revalidateContent({ scope: "branding" });
+    revalidateContent({ scope: "settings" });
+
+    return NextResponse.json({
+      success: true,
+      master: `/branding/${MASTER_FILENAME}`,
+      variants: generated,
+      warnings,
+    });
+  } catch (error: any) {
+    console.error("[favicon] generation failed:", error);
+    return NextResponse.json(
+      { error: error.message || "Favicon generation failed." },
+      { status: 500 }
+    );
+  }
+}

src/app/hq-command/dashboard/settings/page.tsx

@@ -170,16 +170,11 @@ function BrandingTab({
         field. Changes appear on the live site within 60 seconds, no rebuild needed.
       </Tip>
 
-      <ImageField
-        label="Favicon"
-        helper="PNG, square, transparent background. Minimum 512×512. Auto-resized for tabs and bookmarks."
-        value={value.faviconUrl}
-        onChange={(url) => onChange({ ...value, faviconUrl: url })}
-      />
+      <FaviconMasterField />
 
       <ImageField
         label="Apple Touch Icon"
-        helper="PNG, 180×180. Shown when users add the site to their iPhone home screen."
+        helper="Auto-generated from the master favicon above. Override here only if you want a different image for iOS home screens."
         value={value.appleTouchIconUrl}
         onChange={(url) => onChange({ ...value, appleTouchIconUrl: url })}
       />
@@ -495,3 +490,133 @@ function SaveButton({
     </div>
   );
 }
+
+// ─── Favicon master field ────────────────────────────────────────
+// One upload → six PNG variants. Calls /api/branding/favicon which
+// uses sharp to resize the source into 16/32/48/180/192/512 PNGs and
+// drops them under /public/branding/. The root layout auto-detects
+// the variant set and emits the right <link rel="icon"> tags.
+function FaviconMasterField() {
+  const fileInputRef = useRef<HTMLInputElement>(null);
+  const [busy, setBusy] = useState(false);
+  const [result, setResult] = useState<{
+    master?: string;
+    variants?: { url: string; size: number; description: string; bytes: number }[];
+    warnings?: string[];
+    error?: string;
+  } | null>(null);
+
+  // Cache buster: appended to the master preview so re-uploads are visible.
+  const [cacheBust, setCacheBust] = useState(() => Date.now());
+
+  const upload = async (file: File) => {
+    setBusy(true);
+    setResult(null);
+    try {
+      const fd = new FormData();
+      fd.append("file", file);
+      const res = await fetch("/api/branding/favicon", { method: "POST", body: fd });
+      const data = await res.json();
+      if (data.success) {
+        setResult({
+          master: data.master,
+          variants: data.variants,
+          warnings: data.warnings,
+        });
+        setCacheBust(Date.now());
+      } else {
+        setResult({ error: data.error || "Upload failed" });
+      }
+    } catch (err: any) {
+      setResult({ error: err.message || "Upload failed" });
+    }
+    setBusy(false);
+  };
+
+  return (
+    <div className="bg-gradient-to-br from-[#00F0FF]/[0.04] to-transparent border border-[#00F0FF]/20 rounded-2xl p-5">
+      <div className="flex items-start gap-4 mb-4">
+        <div className="w-10 h-10 rounded-xl bg-[#00F0FF]/10 text-[#00F0FF] flex items-center justify-center flex-shrink-0">
+          <ImageIcon size={18} />
+        </div>
+        <div className="flex-1">
+          <div className="text-sm font-medium text-white mb-1">Brand master image → all favicon sizes</div>
+          <div className="text-xs text-[#86868B] leading-relaxed">
+            Upload <strong>one square PNG</strong> at minimum 512×512 (transparent background recommended).
+            We&apos;ll generate every size browsers, iOS, Android and Windows look for —
+            16×16, 32×32, 48×48, 180×180, 192×192, 512×512 — and wire them all into the page head.
+            Re-upload anytime to refresh.
+          </div>
+        </div>
+      </div>
+
+      <div className="flex flex-col md:flex-row md:items-center gap-4">
+        <div className="w-32 h-32 bg-black rounded-xl overflow-hidden border border-white/10 flex items-center justify-center flex-shrink-0">
+          {result?.master ? (
+            // eslint-disable-next-line @next/next/no-img-element
+            <img src={`${result.master}?v=${cacheBust}`} alt="Favicon master" className="w-full h-full object-contain" />
+          ) : (
+            <ImageIcon size={32} className="text-[#86868B]/40" />
+          )}
+        </div>
+
+        <div className="flex-1 space-y-2">
+          <input
+            ref={fileInputRef}
+            type="file"
+            accept="image/png,image/jpeg,image/webp"
+            className="hidden"
+            onChange={(e) => {
+              const file = e.target.files?.[0];
+              if (file) upload(file);
+              e.target.value = "";
+            }}
+          />
+          <button
+            type="button"
+            onClick={() => fileInputRef.current?.click()}
+            disabled={busy}
+            className="inline-flex items-center gap-2 bg-[#00F0FF] text-black hover:bg-[#00F0FF]/80 px-4 py-2.5 rounded-lg text-sm font-medium transition-colors disabled:opacity-50"
+          >
+            {busy ? <Loader2 size={14} className="animate-spin" /> : <Upload size={14} />}
+            {busy ? "Generating variants…" : "Upload master image"}
+          </button>
+
+          {result?.error && (
+            <div className="text-rose-400 text-xs">{result.error}</div>
+          )}
+
+          {result?.warnings && result.warnings.length > 0 && (
+            <div className="text-amber-400 text-xs space-y-1">
+              {result.warnings.map((w, i) => (
+                <div key={i} className="flex items-start gap-1.5">
+                  <Info size={11} className="mt-0.5 flex-shrink-0" /> <span>{w}</span>
+                </div>
+              ))}
+            </div>
+          )}
+
+          {result?.variants && result.variants.length > 0 && (
+            <div className="bg-black/40 border border-white/10 rounded-lg p-3 mt-3">
+              <div className="text-[10px] uppercase tracking-widest text-emerald-400 font-bold mb-2 flex items-center gap-1.5">
+                <Check size={11} /> {result.variants.length} variants generated
+              </div>
+              <div className="grid grid-cols-2 md:grid-cols-3 gap-2">
+                {result.variants.map((v) => (
+                  <div key={v.url} className="bg-white/[0.02] border border-white/5 rounded p-2 flex items-center gap-2">
+                    {/* eslint-disable-next-line @next/next/no-img-element */}
+                    <img src={`${v.url}?v=${cacheBust}`} alt="" className="w-8 h-8 object-contain bg-black rounded" />
+                    <div className="min-w-0">
+                      <div className="text-[11px] text-white font-mono">{v.size}×{v.size}</div>
+                      <div className="text-[9px] text-[#86868B] truncate">{v.description}</div>
+                    </div>
+                  </div>
+                ))}
+              </div>
+            </div>
+          )}
+        </div>
+      </div>
+    </div>
+  );
+}

src/app/manifest.ts

@@ -0,0 +1,28 @@
+// src/app/manifest.ts
+// ─────────────────────────────────────────────────────────────────────────────
+// Web App Manifest. Auto-served by Next.js at /manifest.webmanifest.
+// Tells Android / Chrome / Edge "this site can be added to the home screen,
+// here are the icons and how to launch it standalone".
+// ─────────────────────────────────────────────────────────────────────────────
+
+import type { MetadataRoute } from "next";
+import { getBranding } from "@/lib/siteSettings";
+
+export default async function manifest(): Promise<MetadataRoute.Manifest> {
+  const branding = await getBranding();
+
+  return {
+    name: "FLUX | Energy, Directed.",
+    short_name: "FLUX",
+    description: "Advanced Radio Frequency Solutions by Patrizio Grando.",
+    start_url: "/",
+    display: "standalone",
+    background_color: "#F5F5F7",
+    theme_color: branding.themeColor,
+    icons: [
+      { src: "/branding/favicon-192.png", sizes: "192x192", type: "image/png", purpose: "any" },
+      { src: "/branding/favicon-512.png", sizes: "512x512", type: "image/png", purpose: "any" },
+      { src: "/branding/favicon-512.png", sizes: "512x512", type: "image/png", purpose: "maskable" },
+    ],
+  };
+}