List workspace audio files

Lists the audio files in the API key's workspace, newest first. Use an entry's id as videoSettings.backgroundMusicId (video posts) or postSettings.backgroundMusicId (scheduled reels); audioId, their older name, is still accepted — both take an id, never a URL. Uploading is done in the PostNitro app; this API only lists and deletes. An empty library returns 200 with an empty array. Docs: https://postnitro.ai/docs/embed/api/audio.md