feat: branding asset serving + footer email/phone fields

Two changes that together make Site Settings actually work end-to-end.

BRANDING ASSET SERVING (the broken thumbnails fix)
The favicon/logo previews were broken because uploaded files in
/public/branding had no path to reach the browser:
  1. The folder wasn't mounted into the app container, so uploads
     vanished on next deploy
  2. Nginx had no location block, so /branding/foo.png returned 404
     (everything not in cases/applications/news/parts/footage was a
     proxy_pass to Next.js, which doesn't serve from /public/branding
     in standalone mode)

Fix:
- docker-compose.yml: ./public/branding mounted to /app/public/branding
  (write side) AND /srv/branding (read-only side for Nginx)
- nginx/conf.d/flux.conf: new "location /branding/" block, same
  cache strategy as the other asset locations (max-age=300, must-revalidate)

FOOTER EMAIL + PHONE (David's request)
- siteSettingsTypes.ts: hqEmail and hqPhone fields added to FooterSettings,
  pre-filled with sales@lethepowerflux.com and +39 0424 287 492
- Footer.tsx: clickable mailto: and tel: links with Mail / Phone icons
  shown right under the HQ address. Hidden when fields are empty so the
  layout stays clean for editors who want to suppress contact info.
- /hq-command/dashboard/settings: new "Headquarters contact" group in
  the Footer tab with the two fields (auto-translate ignores them, since
  emails and phone numbers don't need translation).

DEPLOY (David)
  cd /opt/flux-srl
  mkdir -p public/branding   # one-time, creates the folder if missing
  git pull
  docker compose up -d --build app
  docker compose exec nginx nginx -t
  docker compose exec nginx nginx -s reload

nginx/conf.d/flux.conf

@@ -163,6 +163,12 @@ server {
         access_log off;
     }
 
+    location /branding/ {
+        alias /srv/branding/;
+        add_header Cache-Control "public, max-age=300, must-revalidate" always;
+        access_log off;
+    }
+
     location / {
         proxy_pass http://nextjs;
         proxy_set_header Host $host;