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/config/navItems.ts

@@ -3,6 +3,7 @@ import {
   Disc3, Users, Music4, Radio, Heart, BarChart3,
   HelpCircle, Tags, ListMusic, Cast, TrendingUp,
   FolderOpen, HardDriveUpload, Wand2, Shuffle, Dices, Sparkles,
+  AudioLines,
 } from 'lucide-react';
 
 export interface NavItemMeta {
@@ -17,6 +18,7 @@ export const ALL_NAV_ITEMS: Record<string, NavItemMeta> = {
   mainstage:    { icon: Disc3,          labelKey: 'sidebar.mainstage',    to: '/',              section: 'library' },
   newReleases:  { icon: Radio,          labelKey: 'sidebar.newReleases',  to: '/new-releases',  section: 'library' },
   allAlbums:    { icon: Music4,         labelKey: 'sidebar.allAlbums',    to: '/albums',        section: 'library' },
+  tracks:       { icon: AudioLines,     labelKey: 'sidebar.tracks',       to: '/tracks',        section: 'library' },
   randomPicker: { icon: Wand2,          labelKey: 'sidebar.randomPicker', to: '/random',        section: 'library' },
   randomMix:    { icon: Shuffle,        labelKey: 'sidebar.randomMix',    to: '/random/mix',    section: 'library' },
   randomAlbums: { icon: Dices,          labelKey: 'sidebar.randomAlbums', to: '/random/albums', section: 'library' },