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/styles/app.css

@@ -255,6 +255,30 @@ input[type="range"] { width: 100%; accent-color: var(--accent); }
 }
 .modal h2 { margin: 0; font-size: 17px; }
 
+/* --- strip moderation (/admin) ------------------------------------------ */
+.adm { height: 100%; overflow-y: auto; padding: 18px 22px 40px; }
+.adm-bar { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; margin-bottom: 16px; }
+.adm-title { font-size: 15px; letter-spacing: 0.02em; }
+.adm-spacer { flex: 1 1 auto; }
+.adm-note { margin: 12px 0; }
+.adm-sub { margin: 0 0 14px; }
+.adm-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(220px, 1fr)); gap: 12px; }
+.adm-card {
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+  border: 1px solid var(--border);
+  border-radius: var(--radius);
+  background: var(--bg-elev);
+  padding: 10px;
+}
+.adm-card img { width: 100%; aspect-ratio: 4 / 3; object-fit: cover; border-radius: var(--radius-sm); background: var(--bg-sunken); }
+.adm-meta { display: flex; flex-direction: column; gap: 2px; font-size: 11.5px; color: var(--text-dim); min-width: 0; }
+.adm-meta b { color: var(--text); font-family: var(--mono); }
+.adm-meta span { overflow-wrap: anywhere; }
+.adm-danger { color: var(--danger); border-color: var(--border); }
+.adm-danger:hover:not(:disabled) { border-color: var(--danger); }
+
 /* --- responsive --------------------------------------------------------- */
 @media (max-width: 860px) {
   .workspace { flex-direction: column; }