Trakt lists: keep the Radarr/Sonarr lookups of their titles on disk

Library membership is asked every time via movie?tmdbId= / series?tvdbId=;
only the lookups of titles not in the library are stored (3 days).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/radarr/radarr.go

@@ -102,6 +102,19 @@ func (c *Client) Movies(ctx context.Context) ([]Movie, error) {
 	return movies, err
 }
 
+// MovieByTMDB returns the library movie with the TMDb id, ok=false if the
+// library has none. Unlike a lookup it does not ask the metadata provider.
+func (c *Client) MovieByTMDB(ctx context.Context, tmdbID int) (Movie, bool, error) {
+	var movies []Movie
+	err := c.Do(ctx, http.MethodGet, "movie", url.Values{"tmdbId": {strconv.Itoa(tmdbID)}}, nil, &movies)
+	for _, m := range movies { // checked: a version that ignores the filter sends the whole library
+		if m.TMDBID == tmdbID && m.InLibrary() {
+			return m, true, err
+		}
+	}
+	return Movie{}, false, err
+}
+
 // AddOptions are the choices from the add form.
 type AddOptions struct {
 	QualityProfileID    int