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/nb.ts

@@ -21,6 +21,7 @@ export const nbTranslation = {
     cancelDownload: 'Avbryt nedlasting',
     offlineLibrary: 'Frakoblet bibliotek',
     genres: 'Sjangere',
+    tracks: 'Spor',
     playlists: 'Spillelister',
     mostPlayed: 'Mest spilt',
     radio: 'Internettradio',
@@ -377,6 +378,20 @@ export const nbTranslation = {
     offlineQueuing: 'Legger {{count}} album i kø for offline…',
     offlineFailed: 'Kunne ikke legge til {{name}} offline',
   },
+  tracks: {
+    title: 'Spor',
+    subtitle: 'Bla. Søk. Oppdag.',
+    heroEyebrow: 'Sporet akkurat nå',
+    heroReroll: 'Velg et annet',
+    playSong: 'Spill av',
+    enqueueSong: 'Legg til i kø',
+    railRandom: 'Tilfeldig valg',
+    browseTitle: 'Bla gjennom alle spor',
+    browseUnsupported: 'Denne tjeneren lister ikke hele biblioteket på én gang. Bruk søket ovenfor for å finne bestemte spor.',
+    searchPlaceholder: 'Finn et spor etter tittel, artist eller album…',
+    count_one: '{{count}} spor',
+    count_other: '{{count}} spor',
+  },
   artists: {
     title: 'Artister',
     search: 'Søk…',