feat: dedicated 3D Models bucket in AssetBucketBrowser

Add a "3D Models" bucket (path: models, accept: .glb/.gltf/.usdz)
to the cases scope. Previously 3D files were mixed into the Media
bucket at the root. Now they have their own tab with proper file
type hints and purple accent color matching the AR viewer UI.

- cases/media bucket no longer lists .glb/.gltf/.usdz in accept
- New bucketHint for models bucket warns on non-3D file uploads
- Network page 3D tab updated with purple accent + "3D Models"
  button label pointing to the dedicated bucket

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/hq/AssetBucketBrowser.tsx

@@ -57,8 +57,9 @@ export interface BucketDef {
 
 const BUCKETS_BY_SCOPE: Record<Scope, BucketDef[]> = {
   cases: [
-    { id: "media",   path: "",        label: "Media",   description: "Cover, gallery, 3D models — files at the case root", icon: ImageIcon, accept: "image/*,.glb,.gltf,.usdz", accentColor: "#00F0FF" },
+    { id: "media",   path: "",        label: "Media",   description: "Cover and gallery images at the case root",           icon: ImageIcon, accept: "image/*",                  accentColor: "#00F0FF" },
     { id: "videos",  path: "videos",  label: "Videos",  description: "MP4 clips of the installation in operation",          icon: Video,     accept: "video/*",                  accentColor: "#4DA6FF" },
+    { id: "models",  path: "models",  label: "3D Models", description: "GLB/USDZ for AR viewer and 3D display",            icon: Box,       accept: ".glb,.gltf,.usdz",         accentColor: "#A855F7" },
     { id: "renders", path: "renders", label: "Renders", description: "3D rendered images of the equipment",                 icon: Box,       accept: "image/*",                  accentColor: "#FF6B9D" },
   ],
   applications: [
@@ -88,7 +89,8 @@ function bucketHint(bucket: BucketDef, fileName: string): string | null {
   const isModel = ["glb", "gltf", "usdz"].includes(ext);
   if (bucket.id === "videos" && !isVideo) return "Videos bucket usually holds .mp4 — this file may not display correctly.";
   if (bucket.id === "renders" && !isImage) return "Renders bucket expects images (PNG/JPG/WebP).";
-  if (bucket.id === "media" && !isImage && !isVideo && !isModel) return "Most pages expect images, videos or 3D model files here.";
+  if (bucket.id === "models" && !isModel) return "Models bucket expects 3D files (.glb, .gltf, .usdz).";
+  if (bucket.id === "media" && !isImage && !isVideo) return "Media bucket expects images or videos here.";
   return null;
 }