The Jellyfin /Items/{id} endpoint resolved albums, artists, songs and
playlists by id but not genres, so a genre id returned 404. Finamp's
genre "See all" fetches the genre as the track list's parent item, and
that 404 crashed its screen to a blank page after the tracks flashed in.
Add a Genre lookup to resolveItemByID (backed by a new GenreRepository.Get)
so a genre id returns its MusicGenre BaseItemDto, matching real Jellyfin.