refactor: migrate persistence to SQLite, add strict provider mode, and optimize collection lookups

- Replace SharedPreferences with SQLite (AppStateDatabase, LibraryCollectionsDatabase) for download queue, library collections, and recent access history
- Add Set-based O(1) track containment checks for wishlist, loved, and playlist tracks
- Add batch addTracksToPlaylist with PlaylistAddBatchResult
- Go backend: strict mode locks download to selected provider when auto fallback is off
- Go backend: fix extension progress normalization (percent/100) and lifecycle tracking
- Go backend: case-insensitive provider ID matching throughout fallback chain
- Lyrics embedding now respects lyricsMode setting (embed/both/off)
- Debounced queue persistence to reduce write frequency
- Fix shouldUseFallback logic to not be gated by useExtensions

lib/widgets/playlist_picker_sheet.dart

@@ -18,7 +18,9 @@ Future<void> showAddTrackToPlaylistSheet(
     context: context,
     showDragHandle: true,
     builder: (sheetContext) {
-      final playlists = ref.watch(libraryCollectionsProvider).playlists;
+      final playlists = ref.watch(
+        libraryCollectionsProvider.select((state) => state.playlists),
+      );
       return SafeArea(
         child: Column(
           mainAxisSize: MainAxisSize.min,