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>

scripts/check-headings.mjs

@@ -0,0 +1,35 @@
+#!/usr/bin/env node
+// Heading-order guardrail: each page has at least one <h1> and never skips a
+// level going deeper (e.g. h1 → h3 without an h2). Fails (exit 1) on violations.
+//
+//   node scripts/check-headings.mjs
+import { readFileSync, readdirSync } from 'node:fs';
+import { join, dirname } from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const staticDir = join(dirname(fileURLToPath(import.meta.url)), '..', 'static');
+const pages = readdirSync(staticDir).filter((f) => f.endsWith('.html'));
+let problems = 0;
+
+for (const page of pages) {
+    const html = readFileSync(join(staticDir, page), 'utf8');
+    const levels = [...html.matchAll(/<h([1-6])\b/gi)].map((m) => Number(m[1]));
+    if (!levels.length) continue; // heading-less shells (error pages) are fine
+    const issues = [];
+    if (!levels.includes(1)) issues.push('no <h1>');
+    let prev = 0;
+    for (const lvl of levels) {
+        if (prev && lvl > prev + 1) issues.push(`skips h${prev}→h${lvl}`);
+        prev = lvl;
+    }
+    if (issues.length) {
+        problems++;
+        console.error(`${page}: ${issues.join(', ')}  [order: ${levels.join(',')}]`);
+    }
+}
+
+if (problems) {
+    console.error(`\n✖ ${problems} page(s) with heading-order issues.`);
+    process.exit(1);
+}
+console.log('✓ All pages have an h1 and no skipped heading levels.');