feat: a version named after a dash counts as a version, and a song held twice beside a wrong slot no longer blocks it (M498)

- songKey drops a dashed version suffix (" - Instrumental Version", " - Radio
  Edit", live, remix, mix, acoustic, demo, reprise, rework, VIP), so Andora's
  "Goodbye Yesterday - Instrumental Version" is distinct, not a wrong slot.
- wrongSlots accepts several fitting copies when they share one title
  (Killjoy twice beside Dreamland): the other slot's copy is removed, and the
  doubled song is left for the next sweep to find as a pair the resolver merges.

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

internal/library/duplicate_settle.go

@@ -49,8 +49,15 @@ type slotCopy struct {
 // wrongSlots decides which copies of a one-album mismatch sit in a slot that
 // is not theirs. keep is the copy whose slot fits the recording; ok is false
 // when the track list cannot say, and nothing should be removed.
+//
+// Several copies may fit when they carry the same title ("Killjoy" twice
+// beside "Dreamland"): they are one song held twice, not a wrong slot, so they
+// are neither kept nor lost here. Once the wrong slot is emptied, the next
+// sweep finds the pair on its own, and the resolver merges it as any song held
+// twice on one album.
 func wrongSlots(copies []slotCopy, tracks []dbq.MbReleaseTrack) (keep int, losers []int, ok bool) {
 	keep = -1
+	keepKey := ""
 	for i, c := range copies {
 		key := MatchTitleKey(c.Title, c.Artist)
 		fits, other, known := false, true, false
@@ -68,11 +75,12 @@ func wrongSlots(copies []slotCopy, tracks []dbq.MbReleaseTrack) (keep int, loser
 			}
 		}
 		switch {
-		case fits:
-			if keep >= 0 {
+		case fits && keep >= 0:
+			if key != keepKey {
 				return -1, nil, false
 			}
-			keep = i
+		case fits:
+			keep, keepKey = i, key
 		case known && other:
 			losers = append(losers, i)
 		default: