feat(library): show saved animated artwork on local albums

Reuse downloaded motion artwork for local and downloaded album headers, with static fallbacks and reduced-motion support. Opening an album does not trigger an artwork search or download.

lib/providers/player_motion_artwork_provider.dart

@@ -5,8 +5,8 @@ typedef PlayerArtworkAlbum = ({String album, String artist});
 
 final motionArtworkStoreProvider = Provider((ref) => MotionArtworkStore());
 
-/// Playback only reads artwork already saved with a download. Opening a player
-/// must never search other extensions or trigger an artwork download.
+/// Player and local album pages read artwork already saved with a download.
+/// Opening either must never search extensions or download more artwork.
 final playerMotionArtworkProvider = FutureProvider.autoDispose
     .family<MotionArtwork?, PlayerArtworkAlbum>((ref, album) async {
       if (album.album.trim().isEmpty || album.artist.trim().isEmpty) {