fix: same-titled albums of two release groups are two albums, and a missing track with no disc is on disc 1

The scanner found an album by artist and title alone, so Weezer's six
self-titled albums (1994–2026) were one 118-track row and their merges,
wants and upgrades counted them as one. A same-named row whose release group
is known and differs from the file's is now another album; tagReadVersion 7
re-reads the library so existing tracks move to their own rows.

WantHoldings compared discs with IS NOT DISTINCT FROM, so a missing track 6
with no disc was never covered by a present disc 1 track 6. Air's Love 2
stayed wanted and was downloaded again for nothing.

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

internal/library/scanner.go

@@ -74,7 +74,11 @@ var audioExtensions = map[string]bool{
 //	   dhowden/tag reads it as 0, and Minstrel's own importer wrote it that
 //	   way, so all 245 FLAC tracks it imported came in with no track or disc
 //	   number and their albums lost their order.
-const tagReadVersion int16 = 6
+//	7: an album of the same name in another release group gets its own row
+//	   (resolveAlbum). Weezer's six self-titled albums were one 118-track row,
+//	   so their merges, wants and upgrades all counted as one album; a re-read
+//	   files each existing track under its own album.
+const tagReadVersion int16 = 7
 
 type Stats struct {
 	Scanned int `json:"scanned"`
@@ -562,7 +566,12 @@ func (s *Scanner) resolveArtist(ctx context.Context, q *dbq.Queries, name, mbid
 }
 
 func (s *Scanner) resolveAlbum(ctx context.Context, q *dbq.Queries, artistID pgtype.UUID, title string, year int, mbid, releaseGroupMBID string) (dbq.Album, error) {
-	existing, err := q.GetAlbumByArtistAndTitle(ctx, dbq.GetAlbumByArtistAndTitleParams{ArtistID: artistID, Title: title})
+	lookup := dbq.GetAlbumByArtistAndTitleParams{ArtistID: artistID, Title: title}
+	if releaseGroupMBID != "" {
+		rg := releaseGroupMBID
+		lookup.ReleaseGroupMbid = &rg
+	}
+	existing, err := q.GetAlbumByArtistAndTitle(ctx, lookup)
 	if err == nil {
 		// Heal the release group the same way. Not unique, so no conflict to
 		// handle: every release of a group may carry it.