feat(#402): publish album/artist like events on the SSE bus

#392 shipped track.liked / track.unliked but skipped the album +
artist symmetric pairs. Closes that gap so the Flutter Liked tab's
albums and artists sub-lists can listen for changes the same way
the tracks sub-list will (#402 wire-up lands next commit).

publishLikeEvent already handles the entity_type dispatch; the four
handler call sites just need the new lines.

For #402 follow-up to #392.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/api/likes.go

@@ -113,6 +113,7 @@ func (h *handlers) handleLikeAlbum(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	h.logLikeChange(r, syncpkg.EntityLikeAlbum, user.ID, id, syncpkg.OpUpsert)
+	h.publishLikeEvent(user.ID, id, "album", true)
 	w.WriteHeader(http.StatusNoContent)
 }
 
@@ -131,6 +132,7 @@ func (h *handlers) handleUnlikeAlbum(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	h.logLikeChange(r, syncpkg.EntityLikeAlbum, user.ID, id, syncpkg.OpDelete)
+	h.publishLikeEvent(user.ID, id, "album", false)
 	w.WriteHeader(http.StatusNoContent)
 }
 
@@ -159,6 +161,7 @@ func (h *handlers) handleLikeArtist(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	h.logLikeChange(r, syncpkg.EntityLikeArtist, user.ID, id, syncpkg.OpUpsert)
+	h.publishLikeEvent(user.ID, id, "artist", true)
 	w.WriteHeader(http.StatusNoContent)
 }
 
@@ -177,6 +180,7 @@ func (h *handlers) handleUnlikeArtist(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	h.logLikeChange(r, syncpkg.EntityLikeArtist, user.ID, id, syncpkg.OpDelete)
+	h.publishLikeEvent(user.ID, id, "artist", false)
 	w.WriteHeader(http.StatusNoContent)
 }