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/uploadDropdown.css

@@ -7,7 +7,7 @@
 .upload-dropdown .btn-primary {
     display: flex;
     align-items: center;
-    gap: 6px;
+    gap: var(--space-1-5);
 }
 
 .upload-dropdown-menu {
@@ -17,7 +17,7 @@
     left: 0;
     min-width: 200px;
     background: var(--color-bg-surface);
-    border-radius: 12px;
+    border-radius: var(--radius-2xl);
     box-shadow: 0 8px 30px var(--color-shadow-md);
     border: 1px solid var(--color-border);
     z-index: 1000;
@@ -39,13 +39,13 @@
 .upload-dropdown-item {
     display: flex;
     align-items: center;
-    gap: 12px;
+    gap: var(--space-3);
     width: 100%;
-    padding: 12px 16px;
+    padding: var(--space-3) var(--space-4);
     border: none;
     background: none;
     color: var(--color-text-dark);
-    font-size: 14px;
+    font-size: var(--text-base);
     cursor: pointer;
     transition: background 0.15s ease;
     text-align: left;
@@ -71,6 +71,6 @@
 }
 
 .upload-caret {
-    margin-left: 4px;
-    font-size: 12px;
+    margin-left: var(--space-1);
+    font-size: var(--text-xs);
 }