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/library/duplicate_survivor_test.go

@@ -90,11 +90,10 @@ func TestProposeSurvivor_ReasonIsTheDecidingRule(t *testing.T) {
 	}
 }
 
-// M498 #5436: the copy Lidarr maps outranks everything, then the copy whose
-// tags fit the album; quality decides only between copies equal on both. Each
-// case is built so the older rules would choose the other copy, so a reorder
-// that drops the new rules fails.
-func TestProposeSurvivor_LidarrThenTagFit(t *testing.T) {
+// M498 #5436: the copy whose tags fit the album outranks quality, which decides
+// only between copies whose tags fit equally. Each case is built so the quality
+// rules would choose the other copy, so a reorder that drops tag fit fails.
+func TestProposeSurvivor_TagFitFirst(t *testing.T) {
 	at := time.Date(2025, 1, 1, 0, 0, 0, 0, time.UTC)
 	cases := []struct {
 		name       string
@@ -103,12 +102,12 @@ func TestProposeSurvivor_LidarrThenTagFit(t *testing.T) {
 		wantReason string
 	}{
 		{
-			name: "tracked beats lossless and better tags",
+			name: "tag fit beats lossless",
 			cands: []SurvivorCandidate{
-				{TrackID: "flac", FileFormat: "flac", FileSize: 40_000_000, AddedAt: at, TagFit: 3},
-				{TrackID: "tracked", FileFormat: "mp3", FileSize: 5_000_000, AddedAt: at, TagFit: 1, LidarrTracked: true},
+				{TrackID: "flac", FileFormat: "flac", FileSize: 40_000_000, AddedAt: at, TagFit: 1},
+				{TrackID: "fits", FileFormat: "mp3", FileSize: 5_000_000, AddedAt: at, TagFit: 3},
 			},
-			wantID: "tracked", wantReason: "the copy Lidarr tracks",
+			wantID: "fits", wantReason: "tags fit the album",
 		},
 		{
 			// The Humanz shape: two rips a few bytes apart, one carrying a