feat: duplicates resolve themselves without Lidarr (M502 #5517)

Lidarr is off, and with it the resolver had stopped merging: it only
merged when Lidarr had said which copies it mapped. Minstrel is now the
only program writing the library, so the rule is about the copies:

- A song held twice on one album: the extra copies merge into the one
  whose tags fit best (then lossless, larger, older).
- Across releases or under another title: when every copy but one is a
  video rip (held back, or named like one and not marked fine), the rips
  merge into the one that is not.
- Clean copies on different releases are linked as one song, as before.
- Anything else waits for the operator.

Gone with Lidarr: release switches and their settle window, the
unmapped-file read, the rip search, the merge guard and its 409/503,
lidarr.Client's release methods, and duplicate_group_members.lidarr_state
(migration 0078). The duplicates page drops the per-copy Lidarr badge
and the blocked-merge notice; past release changes stay in its history.

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

internal/tracks/service.go

@@ -31,7 +31,6 @@ import (
 	"git.fabledsword.com/bvandeusen/minstrel/internal/audit"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
 	"git.fabledsword.com/bvandeusen/minstrel/internal/library"
-	"git.fabledsword.com/bvandeusen/minstrel/internal/lidarr"
 	syncpkg "git.fabledsword.com/bvandeusen/minstrel/internal/sync"
 )
 
@@ -41,22 +40,6 @@ import (
 // same pointer.
 var ErrNotFound = apierror.ErrNotFound
 
-// ErrLidarrDisabled is what a LidarrUnmonitorer that also lists Lidarr's
-// unmapped files returns when Lidarr is turned off: there is then no Lidarr
-// record a removal could break, and a merge goes ahead unguarded.
-var ErrLidarrDisabled = errors.New("tracks: lidarr disabled")
-
-// ErrLidarrUnavailable means Lidarr is on but did not answer, so a merge cannot
-// confirm the copies it would remove are ones Lidarr does not need (M498), and
-// refuses rather than guess.
-var ErrLidarrUnavailable = errors.New("tracks: lidarr did not answer")
-
-// lidarrFileLister is the optional part of the Lidarr dependency a merge uses to
-// learn which files Lidarr holds without mapping to any track.
-type lidarrFileLister interface {
-	ListUnmappedTrackFiles(ctx context.Context) ([]lidarr.TrackFile, error)
-}
-
 // LidarrUnmonitorer is the subset of *lidarr.Client RemoveTrack uses.
 // Defined as an interface so tests can stub without spinning up a Lidarr
 // httptest server. UnmonitorTrack failures are non-fatal at the service
@@ -168,9 +151,7 @@ func (s *Service) RemoveTrack(
 }
 
 // MergeDuplicates merges a duplicate group into the copy to keep
-// (library.MergeDuplicateGroupGuarded, refusing to remove a copy Lidarr maps:
-// library.ErrCopyTrackedByLidarr, or ErrLidarrUnavailable when Lidarr cannot
-// say), then — when asked — tells Lidarr to stop
+// (library.MergeDuplicateGroup), then — when asked — tells Lidarr to stop
 // monitoring the removed copies so it does not download them again, and records
 // the merge in the audit log.
 //
@@ -180,11 +161,7 @@ func (s *Service) RemoveTrack(
 func (s *Service) MergeDuplicates(
 	ctx context.Context, groupID, survivorID, actorID pgtype.UUID, unmonitor bool,
 ) (res library.MergeResult, lidarrUnmonitorFailed bool, err error) {
-	removable, err := s.lidarrRemovable(ctx)
-	if err != nil {
-		return res, false, err
-	}
-	res, err = library.MergeDuplicateGroupGuarded(ctx, s.pool, s.logger, s.dataDir, groupID, survivorID, removable)
+	res, err = library.MergeDuplicateGroup(ctx, s.pool, s.logger, s.dataDir, groupID, survivorID)
 	if err != nil {
 		return res, false, err
 	}
@@ -226,29 +203,6 @@ func (s *Service) MergeDuplicates(
 	return res, lidarrUnmonitorFailed, nil
 }
 
-// lidarrRemovable is the merge's guard (M498): only a copy Lidarr holds without
-// mapping it to a track may be removed, because removing a mapped one makes
-// Lidarr download it again. Nil, allowing everything, when Lidarr is disabled
-// or the dependency cannot list files.
-func (s *Service) lidarrRemovable(ctx context.Context) (library.RemovableFunc, error) {
-	lister, ok := s.lidarr.(lidarrFileLister)
-	if !ok {
-		return nil, nil
-	}
-	files, err := lister.ListUnmappedTrackFiles(ctx)
-	if errors.Is(err, ErrLidarrDisabled) {
-		return nil, nil
-	}
-	if err != nil {
-		return nil, fmt.Errorf("%w: %v", ErrLidarrUnavailable, err)
-	}
-	unmapped := make(map[string]bool, len(files))
-	for _, f := range files {
-		unmapped[library.LidarrPathKey(f.Path)] = true
-	}
-	return func(p string) bool { return unmapped[library.LidarrPathKey(p)] }, nil
-}
-
 // sameLidarrTrack reports whether two copies are the same Lidarr track: one
 // recording on one album. Lidarr monitors per album track, so when the removed
 // copy is a second file of the kept copy's own album track — the #3885 case —