feat: photo/video capture-date pipeline + premium UI/UX overhaul

Backend — Photos timeline now groups by real capture date instead of upload time. New MediaMetadataService (FileLifecycleHook) extracts EXIF DateTimeOriginal from images and container creation_time from videos (mov/mp4/mkv) via nom-exif, timezone-correct (OffsetTimeOriginal), persisting captured_at so the existing media_sort_date trigger takes over. Adds POST /admin/photos/metadata/reextract to backfill existing media. Falls back to upload date when no embedded date exists.

Frontend — premium grid cards: combined metadata line (relative date · size, owner avatar when shared), custom selection checkbox with a clear checked state, uniform full-width 4:3 thumbnail tiles independent of filename length, centered file-type icons, and a hit-test fix so checkbox/star/kebab clicks reach the controls (the decorative thumbnail no longer captures pointer events). Notification messages internationalised across all 16 locales. Broader polish: design tokens, a11y/focus-visible states, brand + PWA assets.

Chore — bump semver-compatible dependencies (cargo upgrade); add nom-exif 3.6.1.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

static/css/base/forms.css

@@ -4,18 +4,18 @@
 
 .form-group label {
     display: block;
-    margin-bottom: 8px;
-    font-weight: 500;
+    margin-bottom: var(--space-2);
+    font-weight: var(--weight-medium);
     color: var(--color-text-secondary);
 }
 
 .form-group input,
 .form-group textarea {
     width: 100%;
-    padding: 10px;
+    padding: var(--space-2-5);
     border: 1px solid var(--color-border);
-    border-radius: 6px;
-    font-size: 14px;
+    border-radius: var(--radius-md);
+    font-size: var(--text-base);
 }
 
 .form-group textarea {
@@ -24,11 +24,11 @@
 }
 
 .button {
-    padding: 8px 16px;
+    padding: var(--space-2) var(--space-4);
     border: none;
-    border-radius: 6px;
+    border-radius: var(--radius-md);
     cursor: pointer;
-    font-size: 14px;
+    font-size: var(--text-base);
     transition: background-color 0.2s;
 }