PlayerBar reads playbackState + mediaItem streams; hidden when no
queue. Home track-row tap, album play button, album track tap, artist
play button (shuffle) all route to playerActions.playTracks. Token +
baseUrl forwarded to the audio handler before each new queue.
LikedIdsController loads /api/likes/ids once and mutates the local set
on toggle. Failed mutations roll the set back so the icon never lies.
Wired into ArtistDetail header, AlbumDetail header, and per-track in
the album track list.
Headers carry placeholder play buttons (wired in Task 18) + room for
LikeButton (Task 16). Artist screen has a 2-column album grid; album
screen has a track list with mm:ss durations. Routes :id-parameterized
under the shell so the PlayerBar persists.