fix(lidarrquarantine): keep LidarrAlbumMbid nil on Resolve/DeleteFile audit rows + cover idempotent Resolve

The audit log treats lidarr_album_mbid as a 'this row triggered Lidarr'
marker. Setting it on Resolve/DeleteFile (where Lidarr is never contacted)
muddied that semantic. Reverting to plan: only DeleteViaLidarr writes the
mbid. Adds an idempotency test for Resolve over a track with zero rows
(audit row written, affected_users=0, mbid nil).

internal/lidarrquarantine/service_test.go

@@ -253,12 +253,37 @@ func TestResolve_ClearsRowsAndWritesAudit(t *testing.T) {
 	if audit.Action != dbq.LidarrQuarantineActionKindResolved {
 		t.Errorf("action = %v, want resolved", audit.Action)
 	}
+	if audit.LidarrAlbumMbid != nil {
+		t.Errorf("lidarr_album_mbid = %v, want nil for resolve", audit.LidarrAlbumMbid)
+	}
 	n, _ := dbq.New(pool).CountQuarantineForTrack(context.Background(), track.ID)
 	if n != 0 {
 		t.Errorf("rows after resolve = %d, want 0", n)
 	}
 }
 
+func TestResolve_NoExistingRowsStillWritesAudit(t *testing.T) {
+	pool := newPool(t)
+	user := seedUser(t, pool, "alice")
+	track, _, _ := seedTrack(t, pool, "T", "x")
+
+	svc := NewService(pool, lidarrconfig.New(pool), nil)
+	// No flags applied — resolve a track with zero quarantine rows.
+	audit, err := svc.Resolve(context.Background(), track.ID, user.ID)
+	if err != nil {
+		t.Fatalf("Resolve: %v", err)
+	}
+	if audit.AffectedUsers != 0 {
+		t.Errorf("affected_users = %d, want 0", audit.AffectedUsers)
+	}
+	if audit.Action != dbq.LidarrQuarantineActionKindResolved {
+		t.Errorf("action = %v, want resolved", audit.Action)
+	}
+	if audit.LidarrAlbumMbid != nil {
+		t.Errorf("lidarr_album_mbid = %v, want nil for resolve", audit.LidarrAlbumMbid)
+	}
+}
+
 func TestResolve_TrackNotFound(t *testing.T) {
 	pool := newPool(t)
 	user := seedUser(t, pool, "alice")
@@ -305,6 +330,9 @@ func TestDeleteFile_RemovesFileAndAuditsAffected(t *testing.T) {
 	if audit.Action != dbq.LidarrQuarantineActionKindDeletedFile {
 		t.Errorf("action = %v, want deleted_file", audit.Action)
 	}
+	if audit.LidarrAlbumMbid != nil {
+		t.Errorf("lidarr_album_mbid = %v, want nil for delete_file", audit.LidarrAlbumMbid)
+	}
 	if _, err := os.Stat(path); !errors.Is(err, os.ErrNotExist) {
 		t.Errorf("file still exists: %v", err)
 	}