feat(lidarr): LookupArtistByMBID, LookupAlbumByMBID, DeleteAlbum

internal/lidarr/errors.go

@@ -10,4 +10,10 @@ var (
 	ErrLookupFailed   = errors.New("lidarr: lookup failed") // 4xx other than 401/403
 	ErrServerError    = errors.New("lidarr: server error")  // 5xx
 	ErrInvalidPayload = errors.New("lidarr: invalid payload")
+	// ErrNotFound is returned by LookupArtistByMBID and LookupAlbumByMBID
+	// when Lidarr returns 200 with an empty array — i.e., the MBID isn't in
+	// Lidarr's monitored set. Distinguished from network/auth errors so admin
+	// handlers can surface it as `lidarr_album_lookup_failed` (502) instead
+	// of `lidarr_unreachable` (503).
+	ErrNotFound = errors.New("lidarr: not found")
 )