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/manifest.webmanifest

@@ -0,0 +1,42 @@
+{
+  "name": "OxiCloud",
+  "short_name": "OxiCloud",
+  "description": "Fast, private cloud storage built with Rust.",
+  "start_url": "/",
+  "scope": "/",
+  "display": "standalone",
+  "background_color": "#0f172a",
+  "theme_color": "#0f172a",
+  "icons": [
+    {
+      "src": "/logo/logo-plain.svg",
+      "sizes": "any",
+      "type": "image/svg+xml",
+      "purpose": "any"
+    },
+    {
+      "src": "/logo/logo-maskable.svg",
+      "sizes": "any",
+      "type": "image/svg+xml",
+      "purpose": "maskable"
+    },
+    {
+      "src": "/logo/maskable-192.png",
+      "sizes": "192x192",
+      "type": "image/png",
+      "purpose": "maskable"
+    },
+    {
+      "src": "/logo/maskable-512.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "maskable"
+    },
+    {
+      "src": "/logo/maskable-512.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "any"
+    }
+  ]
+}