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>

justfile

@@ -57,6 +57,18 @@ check:
     cargo fmt --all
     cargo clippy --all-features --all-targets -- -D warnings
 
+# Frontend design-system / a11y guardrails — pure Node, no extra deps.
+# Single gate: WCAG contrast, heading order, locale completeness, dead tokens,
+# brand-mark drift.
+# (Also run `stylelint static/css/**/*.css`, `biome check`, `tsc -p jsconfig.json
+#  --noEmit` once node_modules is installed — those need devDependencies.)
+frontend-check:
+    node scripts/check-contrast.mjs
+    node scripts/check-headings.mjs
+    node scripts/check-locales.mjs
+    node scripts/check-dead-tokens.mjs
+    node scripts/check-brand-drift.mjs
+
 # audit security (condition: cargo install cargo-audit)
 audit:
     cargo audit