feat: the same song on several releases counts as one song (M498 #5438)

A single and the album it is on stay two files, since each fulfils its own
release in Lidarr, but they are one song to the listener.

- tracks.song_id links copies; the generated song_key (song_id, else the
  track's own id) is what they share (migration 0076).
- The resolver links each cross-release group every pass (idempotent; only
  with auto-resolve on) and, when a link is new, shares existing likes across
  the song and logs them for sync.
- A like or unlike (web and Subsonic) reaches every copy; each change is
  logged and published so clients update every heart.
- The Liked list and its count show the song once; Shuffle and the mix writer
  take one copy per song.
- A merge keeps the removed copy's song link; "Not the same song" on the
  Across releases tab dismisses the group and undoes the link.

Shared plays ("heard via another copy") are left for a later step.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/subsonic/star.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"net/http"
+	"slices"
 
 	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgtype"
@@ -39,12 +40,13 @@ func (m *mediaHandlers) handleStar(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	if trackID.Valid {
-		rows, err := q.LikeTrack(r.Context(), dbq.LikeTrackParams{UserID: user.ID, TrackID: trackID})
+		// Stars the song: every copy of it (M498 #5438).
+		liked, err := q.LikeTrack(r.Context(), dbq.LikeTrackParams{UserID: user.ID, TrackID: trackID})
 		if err != nil {
 			WriteFail(w, r, ErrGeneric, "Could not star track")
 			return
 		}
-		if rows == 1 {
+		if slices.Contains(liked, trackID) {
 			_ = playevents.CaptureContextualLikeIfPlaying(r.Context(), q, user.ID, trackID, m.logger)
 		}
 	}
@@ -75,7 +77,7 @@ func (m *mediaHandlers) handleUnstar(w http.ResponseWriter, r *http.Request) {
 	params := r.URL.Query()
 	q := dbq.New(m.pool)
 	if t, ok := parseUUID(params.Get("id")); ok {
-		_ = q.UnlikeTrack(r.Context(), dbq.UnlikeTrackParams{UserID: user.ID, TrackID: t})
+		_, _ = q.UnlikeTrack(r.Context(), dbq.UnlikeTrackParams{UserID: user.ID, TrackID: t})
 		_ = playevents.SoftDeleteContextualLikes(r.Context(), q, user.ID, t)
 	}
 	if a, ok := parseUUID(params.Get("albumId")); ok {