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/zh.ts

@@ -21,6 +21,7 @@ export const zhTranslation = {
     cancelDownload: '取消下载',
     offlineLibrary: '离线音乐库',
     genres: '流派',
+    tracks: '曲目',
     playlists: '播放列表',
     mostPlayed: '最常播放',
     radio: '网络电台',
@@ -375,6 +376,20 @@ export const zhTranslation = {
     offlineQueuing: '正在将 {{count}} 张专辑加入离线队列…',
     offlineFailed: '添加 {{name}} 离线失败',
   },
+  tracks: {
+    title: '曲目',
+    subtitle: '浏览。搜索。发现。',
+    heroEyebrow: '此刻精选',
+    heroReroll: '换一首',
+    playSong: '播放',
+    enqueueSong: '加入队列',
+    railRandom: '随机精选',
+    browseTitle: '浏览所有曲目',
+    browseUnsupported: '此服务器不支持一次性列出整个音乐库。使用上方的搜索来查找特定曲目。',
+    searchPlaceholder: '按标题、艺人或专辑搜索…',
+    count_one: '{{count}} 首曲目',
+    count_other: '{{count}} 首曲目',
+  },
   artists: {
     title: '艺术家',
     search: '搜索…',