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/test/likes/like_button_test.dart

@@ -5,6 +5,10 @@ import 'package:flutter_test/flutter_test.dart';
 import 'package:minstrel/api/endpoints/likes.dart';
 import 'package:minstrel/likes/like_button.dart';
 import 'package:minstrel/likes/likes_provider.dart';
+import 'package:minstrel/models/album.dart';
+import 'package:minstrel/models/artist.dart';
+import 'package:minstrel/models/page.dart';
+import 'package:minstrel/models/track.dart';
 import 'package:minstrel/theme/theme_data.dart';
 
 class _ThrowingLikesApi implements LikesApi {
@@ -24,6 +28,19 @@ class _ThrowingLikesApi implements LikesApi {
   Future<({Set<String> artists, Set<String> albums, Set<String> tracks})>
       ids() async =>
           (artists: <String>{}, albums: <String>{}, tracks: <String>{});
+
+  // The list-* methods aren't exercised by this test; return empty pages.
+  @override
+  Future<Paged<TrackRef>> listTracks({int limit = 50, int offset = 0}) async =>
+      const Paged<TrackRef>(items: [], total: 0, limit: 50, offset: 0);
+
+  @override
+  Future<Paged<AlbumRef>> listAlbums({int limit = 50, int offset = 0}) async =>
+      const Paged<AlbumRef>(items: [], total: 0, limit: 50, offset: 0);
+
+  @override
+  Future<Paged<ArtistRef>> listArtists({int limit = 50, int offset = 0}) async =>
+      const Paged<ArtistRef>(items: [], total: 0, limit: 50, offset: 0);
 }
 
 void main() {