"""Service layer for the User Favourites feature.

Every module here depends only on an injected ``client`` object exposing four
async methods (``get``, ``get_all``, ``post``, ``delete``). Production code passes
an adapter around the existing Emby helpers in ``app.py``; tests pass a fake. This
keeps the services free of FastAPI/Emby/Pillow import weight and fully unit
testable.
"""