Unify favourite writes through SyncUserFavorite so remote mounted media is
stored locally and proxied to the upstream Emby server. Emby clients now
query favourites from the local table (including remote pseudo IDs), and
remote item payloads merge local IsFavorite state.
Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: truewhile <truewhile@users.noreply.github.com>