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/brandLogo.css

@@ -0,0 +1,24 @@
+/* ============================================================
+ * Canonical brand mark — the OxiCloud cloud glyph on the accent
+ * gradient tile. Reusable lockup for external surfaces (share,
+ * device-verify) so they present the real mark, not text/emoji.
+ * Uses the single --color-logo-gradient token.
+ * ============================================================ */
+
+.brand-mark {
+    width: 56px;
+    height: 56px;
+    border-radius: var(--radius-3xl);
+    background: var(--color-logo-gradient);
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    margin-bottom: var(--space-3);
+    box-shadow: 0 4px 14px var(--color-accent-shadow);
+}
+
+.brand-mark svg {
+    width: 32px;
+    height: 32px;
+    fill: var(--color-on-accent);
+}