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/base/reset.css

@@ -1,13 +1,21 @@
+/* Honor the user's browser font-size / zoom preference (rem-relative). */
+html {
+    font-size: 100%;
+}
+
 * {
     box-sizing: border-box;
     margin: 0;
     padding: 0;
-    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Open Sans", "Helvetica Neue", sans-serif;
+    font-family: var(--font-sans);
 }
 
 body {
     display: flex;
-    height: 100vh;
+    height: 100vh; /* fallback for browsers without dvh */
+    height: 100dvh;
+    font-size: var(--text-base);
+    line-height: var(--leading-normal);
     background-color: var(--color-bg-page);
     overflow: hidden;
 }
@@ -24,3 +32,26 @@ html[dir="rtl"] .fa-sign-out-alt {
 .hidden {
     display: none !important;
 }
+
+/* Brand-tinted text selection + caret. */
+::selection {
+    background: var(--color-accent-ring-strong);
+    color: var(--color-text-heading);
+}
+
+:root {
+    caret-color: var(--color-accent);
+}
+
+/* Visually hidden but exposed to assistive tech (a11y-only labels/headings). */
+.sr-only {
+    position: absolute;
+    width: 1px;
+    height: 1px;
+    padding: 0;
+    margin: -1px;
+    overflow: hidden;
+    clip: rect(0, 0, 0, 0);
+    white-space: nowrap;
+    border: 0;
+}