chore: production readiness audit

- Move plans/ to dev-docs/, delete unused scaffold SVGs
- Create .dockerignore, rename container to immich-folio
- Extract BackLink component and toPhotoItems() helper in page.tsx
- Add keyboard accessibility (role=button, tabIndex, onKeyDown) to PhotoGrid
- Add aria-label to Lightbox EXIF toggle
- Fix React lint: replace setState-in-effect with useState initializer
- Add rate limiting to /api/auth (brute-force protection, 10 RPM)
- Add HSTS and X-DNS-Prefetch-Control security headers
- Add Secure flag to auth cookie in production
- New unit tests: rate-limit.test.ts (5), auth.test.ts (12)
- All 47 tests pass, 0 lint errors, build clean

app/globals.css

@@ -279,10 +279,12 @@
   flex-direction: column;
   justify-content: flex-end;
   padding: 24px;
-  background: linear-gradient(to top,
-      rgba(0, 0, 0, 0.8) 0%,
-      rgba(0, 0, 0, 0.3) 40%,
-      transparent 100%);
+  background: linear-gradient(
+    to top,
+    rgba(0, 0, 0, 0.8) 0%,
+    rgba(0, 0, 0, 0.3) 40%,
+    transparent 100%
+  );
   opacity: 0;
   transition: opacity var(--transition-normal);
 }
@@ -412,10 +414,12 @@
 
 /* ── Loading States ───────────────────────────────── */
 .skeleton {
-  background: linear-gradient(90deg,
-      var(--bg-card) 0%,
-      var(--bg-card-hover) 50%,
-      var(--bg-card) 100%);
+  background: linear-gradient(
+    90deg,
+    var(--bg-card) 0%,
+    var(--bg-card-hover) 50%,
+    var(--bg-card) 100%
+  );
   background-size: 200% 100%;
   animation: skeleton-shimmer 1.5s infinite;
   border-radius: var(--radius-sm);
@@ -434,7 +438,9 @@
 /* ── Fade-In Animations ────────────────────────────── */
 .fade-in {
   opacity: 0;
-  transition: opacity 0.6s ease, transform 0.6s ease;
+  transition:
+    opacity 0.6s ease,
+    transform 0.6s ease;
 }
 
 .fade-in--up {
@@ -724,7 +730,9 @@
   font-weight: 400;
   padding: 6px 0;
   border-bottom: 1px solid transparent;
-  transition: border-color var(--transition-fast), color var(--transition-fast);
+  transition:
+    border-color var(--transition-fast),
+    color var(--transition-fast);
 }
 
 .hero__nav-link:hover {
@@ -841,4 +849,4 @@
   .photo-grid__item {
     padding: 6px 6px 18px;
   }
-}
+}