feat(tracks): add Tracks library hub page (closes #299) (#300)

New /tracks route with three sections:

- Hero "Track of the moment" — random pick with play / enqueue / reroll
- Random Pick rail — 18 song cards, rerollable; hero song deduped
- Browse all tracks — virtualized list (@tanstack/react-virtual),
  paginated 50 at a time

Browse uses Navidrome's native /api/song?_sort=title&_order=ASC for
proper A-Z order (no Subsonic equivalent), with automatic fallback
to search3 on non-Navidrome servers. Search input drives search3
with 300ms debounce. Bearer token cached module-level, re-auth on 401.

Play button on rows + cards calls a new enqueueAndPlay() helper that
appends to the existing queue (skip if duplicate) and jumps to the
song — different from playSongNow which replaces the queue. Enqueue
button stays opaque (no hover-only).

i18n keys for sidebar.tracks + tracks.* namespace in all 8 locales.
New AudioLines sidebar icon. Sidebar entry inserted between
"All Albums" and "Build a Mix".

Performance: cover thumbnails dropped (uniform layout instead),
RAF-throttled scroll prefetch, hover transforms removed from cards
(WebKitGTK compositing-friendly).

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/locales/en.ts

@@ -22,6 +22,7 @@ export const enTranslation = {
     cancelDownload: 'Cancel download',
     offlineLibrary: 'Offline Library',
     genres: 'Genres',
+    tracks: 'Tracks',
     playlists: 'Playlists',
     smartPlaylists: 'Smart Playlists',
     mostPlayed: 'Most Played',
@@ -379,6 +380,20 @@ export const enTranslation = {
     offlineQueuing: 'Queuing {{count}} album(s) for offline…',
     offlineFailed: 'Failed to add {{name}} offline',
   },
+  tracks: {
+    title: 'Tracks',
+    subtitle: 'Browse. Search. Discover.',
+    heroEyebrow: 'Track of the moment',
+    heroReroll: 'Pick another',
+    playSong: 'Play',
+    enqueueSong: 'Add to queue',
+    railRandom: 'Random Pick',
+    browseTitle: 'Browse all tracks',
+    browseUnsupported: "This server doesn't list the whole library at once. Use the search above to find specific tracks.",
+    searchPlaceholder: 'Find a track by title, artist or album…',
+    count_one: '{{count}} track',
+    count_other: '{{count}} tracks',
+  },
   artists: {
     title: 'Artists',
     search: 'Search…',