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>

cmd/minstrel/main.go

@@ -325,18 +325,12 @@ func run() error {
 	library.SetNotifier(notifier)
 	go lidarrReconciler.Run(ctx)
 
-	// Duplicate resolver (M498): classifies the sweep's groups and, with the
-	// operator's auto-resolve on, merges copies Lidarr does not map and moves a
-	// Lidarr release that lists songs twice. Started after SetNotifier so its
-	// summaries reach admins. See internal/library/duplicate_resolve.go.
-	resolverLidarr := func() library.LidarrLibrary {
-		if c := lidarrClientFn(); c != nil {
-			return c
-		}
-		return nil // a nil *lidarr.Client must not become a non-nil interface
-	}
+	// Duplicate resolver (M498, M502): classifies the sweep's groups and, with
+	// the operator's auto-resolve on, merges the copies that are safe to merge.
+	// Started after SetNotifier so its summaries reach admins. See
+	// internal/library/duplicate_resolve.go.
 	go library.NewDuplicateResolveWorker(pool, logger.With("component", "duplicate_resolve"),
-		cfg.Storage.DataDir, fpSettings, resolverLidarr).Run(ctx)
+		cfg.Storage.DataDir, fpSettings).Run(ctx)
 
 	// Missing-file re-acquisition (milestone #290). Turns albums whose files
 	// have been gone longer than the grace window into Lidarr requests, on an