feat(flutter): library screen with 5 tabs (Artists/Albums/History/Liked/Hidden)

Models:
- history_event.dart (HistoryEvent + HistoryPage envelope)
- quarantine_mine.dart (QuarantineMineRow for /api/quarantine/mine)
- Renamed Page<T> -> Paged<T> to avoid collision with Material's Page

Endpoints:
- library_lists.dart: listArtists / listAlbums (paged)
- me.dart: history + quarantineMine
- likes.dart: extended with listTracks/Albums/Artists (paged)

UI:
- library_screen.dart: TabBar over 5 tabs
- Artists tab: 3-col grid
- Albums tab: 2-col grid
- History tab: list with relative-time formatting (matches HistoryRow.svelte)
- Liked tab: 3 stacked sections (artists scroll-row, albums scroll-row, tracks list)
- Hidden tab: list of quarantined tracks with reason pill
- /library route + library_music icon on home AppBar

First page only for v1 (limit 50). Infinite scroll deferred.

flutter_client/lib/shared/routing.dart

@@ -8,6 +8,7 @@ import '../auth/server_url_screen.dart';
 import '../library/album_detail_screen.dart';
 import '../library/artist_detail_screen.dart';
 import '../library/home_screen.dart';
+import '../library/library_screen.dart';
 import '../player/now_playing_screen.dart';
 import '../player/player_bar.dart';
 import '../playlists/playlist_detail_screen.dart';
@@ -55,6 +56,7 @@ GoRouter buildRouter(Ref ref) {
           ),
           GoRoute(path: '/now-playing', builder: (_, __) => const NowPlayingScreen()),
           GoRoute(path: '/search', builder: (_, __) => const SearchScreen()),
+          GoRoute(path: '/library', builder: (_, __) => const LibraryScreen()),
           GoRoute(path: '/playlists', builder: (_, __) => const PlaylistsListScreen()),
           GoRoute(
             path: '/playlists/:id',