plexapi/mixins.py Core implementation: Added delete methods for images/themes, implemented logo locking, added logo property, and updated setLogo() from raising NotImplementedError to selecting logos plexapi/audio.py Added LogoMixin and LogoUrlMixin to Artist, Album, and Track classes plexapi/collection.py Added LogoMixin to Collection class plexapi/photo.py Added LogoMixin and LogoUrlMixin to Photoalbum and Photo classes plexapi/playlist.py Added LogoMixin to Playlist class tests/test_mixins.py Added test helpers for logo operations and delete functionality validation tests/test_video.py Added logo test coverage for Movie, Show, Season, and Episode; uncommented previously disabled Episode art test tests/test_audio.py Added logo test coverage for Artist, Album, and Track tests/test_collection.py Added logo test coverage for Collection tests/test_photo.py Added logo test coverage for Photoalbum tests/test_playlist.py Added logo test coverage for Playlist