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/js/app/uiNotifications.js

@@ -4,6 +4,7 @@
  */
 
 import { notifications } from '../core/notifications.js';
+import { announce } from '../core/liveRegion.js';
 
 const uiNotifications = {
     /**
@@ -40,6 +41,10 @@ const uiNotifications = {
             title: title || '',
             text: message || ''
         });
+
+        // Announce to screen readers — errors interrupt, everything else is polite.
+        const spoken = [title, message].filter(Boolean).join('. ');
+        announce(spoken, { assertive: iconClass === 'error' });
         return;
     }
 };