feat(database): add Playlists, Favorites, PlaybackHistory tables

- Playlists + PlaylistSongs tables with position-ordered join query
- Favorites table with toggle + watch (reactive heart icon support)
- PlaybackHistory table for resume-position tracking
- Schema v2 with migration from v1
- Follows existing Songs/Folders sync-ready pattern (uuid id, updatedAtMs, deleted)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

lib/library/database.dart

@@ -4,6 +4,7 @@ import 'package:drift/drift.dart';
 import 'package:drift/native.dart';
 import 'package:path/path.dart' as p;
 import 'package:path_provider/path_provider.dart';
+import 'package:uuid/uuid.dart';
 
 part 'database.g.dart';
 
@@ -36,12 +37,68 @@ class Folders extends Table {
   Set<Column> get primaryKey => {id};
 }
 
-@DriftDatabase(tables: [Songs, Folders])
+/// Nutzer-Playlisten.
+class Playlists extends Table {
+  TextColumn get id => text()(); // uuid
+  TextColumn get name => text()();
+  TextColumn get description => text().nullable()();
+  IntColumn get createdAtMs => integer()();
+  IntColumn get updatedAtMs => integer()();
+  BoolColumn get deleted => boolean().withDefault(const Constant(false))();
+
+  @override
+  Set<Column> get primaryKey => {id};
+}
+
+/// Zuordnung Song ↔ Playlist mit Reihenfolge.
+class PlaylistSongs extends Table {
+  TextColumn get playlistId => text().references(Playlists, #id)();
+  TextColumn get songId => text().references(Songs, #id)();
+  IntColumn get position => integer()();
+  IntColumn get addedAtMs => integer()();
+
+  @override
+  Set<Column> get primaryKey => {playlistId, songId};
+}
+
+/// Favorisierte Songs.
+class Favorites extends Table {
+  TextColumn get songId => text().references(Songs, #id)();
+  IntColumn get createdAtMs => integer()();
+
+  @override
+  Set<Column> get primaryKey => {songId};
+}
+
+/// Wiedergabe-Historie: letzte Position pro Song (für Resume) + Verlauf.
+class PlaybackHistory extends Table {
+  TextColumn get songId => text().references(Songs, #id)();
+  IntColumn get positionMs => integer()();
+  IntColumn get playedAtMs => integer()();
+
+  @override
+  Set<Column> get primaryKey => {songId, playedAtMs};
+}
+
+@DriftDatabase(tables: [Songs, Folders, Playlists, PlaylistSongs, Favorites, PlaybackHistory])
 class MeloDb extends _$MeloDb {
   MeloDb([QueryExecutor? executor]) : super(executor ?? _open());
 
   @override
-  int get schemaVersion => 1;
+  int get schemaVersion => 2;
+
+  @override
+  MigrationStrategy get migration => MigrationStrategy(
+        onCreate: (m) => m.createAll(),
+        onUpgrade: (m, from, to) async {
+          if (from < 2) {
+            await m.createTable(playlists);
+            await m.createTable(playlistSongs);
+            await m.createTable(favorites);
+            await m.createTable(playbackHistory);
+          }
+        },
+      );
 
   /// Überwacht alle Songs (nicht getombstonte). Nach Titel sortiert.
   Stream<List<Song>> watchSongs() {
@@ -109,6 +166,116 @@ class MeloDb extends _$MeloDb {
 
   Future<void> addFolder(FoldersCompanion folder) =>
       into(folders).insert(folder, onConflict: DoUpdate((_) => folder, target: [folders.path]));
+
+  static const _uuid = Uuid();
+
+  // === Playlists ===
+  Stream<List<Playlist>> watchPlaylists() =>
+      (select(playlists)
+            ..where((p) => p.deleted.equals(false))
+            ..orderBy([(p) => OrderingTerm(expression: p.createdAtMs, mode: OrderingMode.desc)]))
+          .watch();
+
+  Future<String> createPlaylist(String name, {String? description}) async {
+    final id = _uuid.v4();
+    final now = DateTime.now().millisecondsSinceEpoch;
+    await into(playlists).insert(PlaylistsCompanion.insert(
+      id: id,
+      name: name,
+      description: Value(description),
+      createdAtMs: now,
+      updatedAtMs: now,
+    ));
+    return id;
+  }
+
+  Future<void> deletePlaylist(String id) async {
+    await (update(playlists)..where((p) => p.id.equals(id))).write(
+      PlaylistsCompanion(
+        deleted: const Value(true),
+        updatedAtMs: Value(DateTime.now().millisecondsSinceEpoch),
+      ),
+    );
+  }
+
+  // === PlaylistSongs ===
+  Stream<List<Song>> watchPlaylistSongs(String playlistId) {
+    final query = select(songs).join([
+      innerJoin(playlistSongs, playlistSongs.songId.equalsExp(songs.id)),
+    ])
+      ..where(playlistSongs.playlistId.equals(playlistId))
+      ..orderBy([OrderingTerm(expression: playlistSongs.position)]);
+    return query.watch().map((rows) => rows.map((r) => r.readTable(songs)).toList());
+  }
+
+  Future<void> addSongToPlaylist(String playlistId, String songId, int position) async {
+    await into(playlistSongs).insert(
+      PlaylistSongsCompanion.insert(
+        playlistId: playlistId,
+        songId: songId,
+        position: position,
+        addedAtMs: DateTime.now().millisecondsSinceEpoch,
+      ),
+      mode: InsertMode.insertOrReplace,
+    );
+  }
+
+  Future<void> removeSongFromPlaylist(String playlistId, String songId) async {
+    await (delete(playlistSongs)
+          ..where((ps) => ps.playlistId.equals(playlistId) & ps.songId.equals(songId)))
+        .go();
+  }
+
+  Future<void> reorderPlaylistSong(String playlistId, String songId, int newPosition) async {
+    await (update(playlistSongs)
+          ..where((ps) => ps.playlistId.equals(playlistId) & ps.songId.equals(songId)))
+        .write(PlaylistSongsCompanion(position: Value(newPosition)));
+  }
+
+  // === Favorites ===
+  Future<void> toggleFavorite(String songId) async {
+    final existing = await (select(favorites)..where((f) => f.songId.equals(songId))).getSingleOrNull();
+    if (existing == null) {
+      await into(favorites).insert(FavoritesCompanion.insert(
+        songId: songId,
+        createdAtMs: DateTime.now().millisecondsSinceEpoch,
+      ));
+    } else {
+      await (delete(favorites)..where((f) => f.songId.equals(songId))).go();
+    }
+  }
+
+  Stream<bool> watchIsFavorite(String songId) {
+    return (select(favorites)..where((f) => f.songId.equals(songId)))
+        .watchSingleOrNull()
+        .map((row) => row != null);
+  }
+
+  Stream<List<Song>> watchFavorites() {
+    final query = select(songs).join([
+      innerJoin(favorites, favorites.songId.equalsExp(songs.id)),
+    ])
+      ..orderBy([OrderingTerm(expression: favorites.createdAtMs, mode: OrderingMode.desc)]);
+    return query.watch().map((rows) => rows.map((r) => r.readTable(songs)).toList());
+  }
+
+  // === Playback History ===
+  Future<void> recordPlayback(String songId, int positionMs) async {
+    await into(playbackHistory).insert(PlaybackHistoryCompanion.insert(
+      songId: songId,
+      positionMs: positionMs,
+      playedAtMs: DateTime.now().millisecondsSinceEpoch,
+    ));
+  }
+
+  Future<int?> lastPosition(String songId) async {
+    final row = await (select(playbackHistory)
+          ..where((h) => h.songId.equals(songId))
+          ..orderBy([(h) => OrderingTerm(expression: h.playedAtMs, mode: OrderingMode.desc)])
+          ..limit(1))
+        .getSingleOrNull();
+    return row?.positionMs;
+  }
 }
 
 LazyDatabase _open() {