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/models/page.dart

@@ -1,6 +1,8 @@
-// Mirrors the server's Page<T> envelope used by paged endpoints
+// Mirrors the server's Page[T] envelope used by paged endpoints
 // (/api/search, /api/library/artists, /api/library/albums,
-// /api/library/history, /api/me/likes/*).
+// /api/likes/*). Class is named `Paged<T>` rather than `Page<T>`
+// to avoid ambiguous imports with Flutter Material's Navigator-2.0
+// `Page` class.
 //
 // Wire shape from internal/api/types.go Page[T]:
 //   { items: T[], total: int, limit: int, offset: int }
@@ -8,8 +10,8 @@
 // Dart generics can't auto-infer T from JSON, so callers pass an
 // itemFromJson function alongside the raw map. Parse logic stays in
 // each entity's own fromJson; this class only handles the envelope.
-class Page<T> {
-  const Page({
+class Paged<T> {
+  const Paged({
     required this.items,
     required this.total,
     required this.limit,
@@ -21,12 +23,12 @@ class Page<T> {
   final int limit;
   final int offset;
 
-  factory Page.fromJson(
+  factory Paged.fromJson(
     Map<String, dynamic> j,
     T Function(Map<String, dynamic>) itemFromJson,
   ) {
     final raw = (j['items'] as List?) ?? const [];
-    return Page<T>(
+    return Paged<T>(
       items: raw
           .map((e) => itemFromJson((e as Map).cast<String, dynamic>()))
           .toList(growable: false),