fix: a duplicate fold never deletes a lossless copy for a lossy one, nor folds two versions (M498)

The first album-copy fold pass on 2026-10-20 removed five FLACs (Måneskin
Rush!, Weezer 2016) in favour of mp3s whose only edge was a recording MBID,
and an explicit "Suite-Pee" for its clean version. ProposeSurvivor now ranks
lossless before tag fit; tag fit still outranks file size, which is what the
Humanz rips needed. The fold keys copies by their version words (title and
file name), so a clean, live or instrumental copy holding the same title tag
is linked, not folded.

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

internal/api/admin_duplicates_test.go

@@ -65,14 +65,15 @@ func TestFoldDuplicateGroups(t *testing.T) {
 }
 
 // M498: the proposal shown beside a group follows the resolver's rule. The copy
-// whose tags fit the album is proposed even when the other is lossless.
+// whose tags fit the album is proposed even when the other is larger (only a
+// lossless copy outranks it).
 func TestFoldDuplicateGroups_ProposesTheCopyWhoseTagsFit(t *testing.T) {
 	at := time.Date(2025, 1, 1, 0, 0, 0, 0, time.UTC)
 	class := "same_release"
 	three := int32(3)
 	rows := []dbq.ListPendingDuplicateGroupMembersRow{
 		{GroupID: dupUUID(3), Tier: "acoustic", DetectedAt: dupTS(at), TrackID: dupUUID(30), Class: &class,
-			Title: "Song", FileFormat: "flac", FileSize: 30_000_000, AddedAt: dupTS(at)},
+			Title: "Song", FileFormat: "m4a", FileSize: 30_000_000, AddedAt: dupTS(at)},
 		{GroupID: dupUUID(3), Tier: "acoustic", DetectedAt: dupTS(at), TrackID: dupUUID(31), Class: &class,
 			Title: "Song", FileFormat: "mp3", FileSize: 9_000_000, AddedAt: dupTS(at), TrackNumber: &three, HasMbid: true},
 	}