Two new helpers in internal/playevents (CaptureContextualLikeIfPlaying,
SoftDeleteContextualLikes) called by both api and subsonic surfaces.
Like inserts a new contextual_likes row when LikeTrack actually
inserted (rows=1) AND there's an open play_event with a vector.
Unlike soft-deletes via deleted_at. Idempotent in both directions.
Subsonic wiring lands in the next commit.
Like/unlike are POST/DELETE on /api/likes/{type}/{id}; idempotent (204
on repeats). List endpoints return Page<TrackRef|AlbumRef|ArtistRef>
sorted liked_at DESC. /api/likes/ids returns flat id arrays for the
client-side heart-button cache.
bvandeusen