Adds 'Audiobooks' and 'Podcasts' options to the library-type dropdown in the admin libraries page so operators can flag a folder as an audiobook or podcast library. Extends contentLevelsForType() so the admin UI's downstream filtering treats those types correctly (audiobook -> ['audiobook'], podcasts -> ['podcast', 'podcast_episode']). Backend scanner branches for these types were already wired in sub-plan 2. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>