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/song_link_test.go

@@ -78,7 +78,7 @@ func TestCrossReleaseCopiesCountAsOneSong_Integration(t *testing.T) {
 	q := dbq.New(pool)
 	f := newSongLinkFixture(t, pool)
 
-	res, err := ResolveDuplicates(ctx, pool, nil, "", nil, true)
+	res, err := ResolveDuplicates(ctx, pool, nil, "", true)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -118,7 +118,7 @@ func TestCrossReleaseCopiesCountAsOneSong_Integration(t *testing.T) {
 	}
 
 	// A second pass changes nothing.
-	if res, err := ResolveDuplicates(ctx, pool, nil, "", nil, true); err != nil || res.SongsLinked != 0 {
+	if res, err := ResolveDuplicates(ctx, pool, nil, "", true); err != nil || res.SongsLinked != 0 {
 		t.Errorf("second pass linked %d (%v), want 0", res.SongsLinked, err)
 	}
 
@@ -155,7 +155,7 @@ func TestCrossReleaseLinkNeedsAutoResolve_Integration(t *testing.T) {
 	ctx := context.Background()
 	q := dbq.New(pool)
 	f := newSongLinkFixture(t, pool)
-	if _, err := ResolveDuplicates(ctx, pool, nil, "", nil, false); err != nil {
+	if _, err := ResolveDuplicates(ctx, pool, nil, "", false); err != nil {
 		t.Fatal(err)
 	}
 	keys := songKeys(t, q, f.single.ID, f.albumCut.ID)