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/components/contextMenu.css

@@ -7,7 +7,7 @@
     box-shadow:
         0 10px 36px var(--color-shadow-lg),
         0 0 0 1px var(--color-shadow-xs);
-    padding: 6px;
+    padding: var(--space-1-5);
     min-width: 200px;
     z-index: 2000;
     display: block;
@@ -26,14 +26,14 @@
 }
 
 .context-menu-item {
-    padding: 10px 14px;
+    padding: var(--space-2-5) var(--space-3-5);
     cursor: pointer;
     display: flex;
     align-items: center;
-    gap: 12px;
+    gap: var(--space-3);
     color: var(--color-text-dark);
-    font-size: 14px;
-    border-radius: 8px;
+    font-size: var(--text-base);
+    border-radius: var(--radius-lg);
     transition: background 0.12s ease;
 }
 
@@ -48,7 +48,7 @@
 .context-menu-item i {
     width: 18px;
     text-align: center;
-    font-size: 14px;
+    font-size: var(--text-base);
     color: var(--color-text-subtle);
 
     [dir="rtl"] & {
@@ -72,5 +72,5 @@
 .context-menu-separator {
     height: 1px;
     background: var(--color-border-light);
-    margin: 4px 8px;
+    margin: var(--space-1) var(--space-2);
 }