feat(api): add /api/likes/{tracks,albums,artists} endpoints

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.

internal/api/api.go

@@ -36,6 +36,16 @@ func Mount(r chi.Router, pool *pgxpool.Pool, logger *slog.Logger, events *playev
 			authed.Get("/search", h.handleSearch)
 			authed.Get("/radio", h.handleRadio)
 			authed.Post("/events", h.handleEvents)
+			authed.Post("/likes/tracks/{id}", h.handleLikeTrack)
+			authed.Delete("/likes/tracks/{id}", h.handleUnlikeTrack)
+			authed.Post("/likes/albums/{id}", h.handleLikeAlbum)
+			authed.Delete("/likes/albums/{id}", h.handleUnlikeAlbum)
+			authed.Post("/likes/artists/{id}", h.handleLikeArtist)
+			authed.Delete("/likes/artists/{id}", h.handleUnlikeArtist)
+			authed.Get("/likes/tracks", h.handleListLikedTracks)
+			authed.Get("/likes/albums", h.handleListLikedAlbums)
+			authed.Get("/likes/artists", h.handleListLikedArtists)
+			authed.Get("/likes/ids", h.handleGetLikedIDs)
 		})
 	})
 }