feat(photos): community film strip uploads + admin moderation

Backend
- photos table + upload storage under DATA_DIR/uploads (magic-byte sniffing,
  no multipart dep, SVG rejected, wx exclusive writes)
- POST/GET /api/photos, GET /api/photos/:id/file with nosniff + sandboxed CSP
- admin routes (ADMIN_EMAILS allowlist): list, delete one, clear all
- identity-keyed rate limits (login 20/15m, signup 5/h, upload 60/h)
- cookie gains Secure when the request is https (via trustProxy)
- /api/auth/me now 200 {user:null} instead of 401 when signed out

Frontend
- landing strip section: signed-in users upload straight from the reel,
  guests get a /app?auth=1 link
- /admin page: grid of uploads with delete + clear all
- nginx: nosniff / X-Frame-Options / Referrer-Policy, forward
  X-Forwarded-Proto so the API can mark cookies Secure behind TLS

Tests: docker/backend test/security.mjs (45 checks)

docker/frontend/src/i18n/en.ts

@@ -107,6 +107,26 @@ export const en: Dict = {
   'save.saved': 'Saved "{name}"',
   'save.needLogin': 'Log in to save a recipe.',
 
+  'photo.contribute': 'CONTRIBUTE A PHOTO',
+  'photo.uploading': 'UPLOADING…',
+  'photo.thanks': 'Your frame is in the strip.',
+  'photo.failed': 'Upload failed: {msg}',
+
+  'adm.title': 'Strip moderation',
+  'adm.subtitle': 'Photos contributed by users. Delete one to pull it off the landing page.',
+  'adm.signIn': 'Sign in with an admin account',
+  'adm.notAdmin': 'This account has no admin rights.',
+  'adm.empty': 'No contributions yet.',
+  'adm.total': '{n} photos',
+  'adm.owner': 'Uploaded by',
+  'adm.size': 'Size',
+  'adm.uploaded': 'Uploaded',
+  'adm.delete': 'DELETE',
+  'adm.clearAll': 'DELETE ALL',
+  'adm.clearConfirm': 'Delete all {n} contributions? This cannot be undone.',
+  'adm.removed': 'Deleted {n} photos.',
+  'adm.back': 'Back to home',
+
   'err.noWebgl':
     'The browser refused a WebGL context — this build needs WebGL to process photos (the CPU path is thousands of times slower).',
   'err.decode': 'Could not read this image. Try another JPG or PNG.',