Support Instagram Reels audio and TikTok song_clip_id when publishing

Problem

There's no way to attach platform-native music to a post through the API. Our users have to leave the scheduling flow entirely and publish through the Instagram/Edits app or the TikTok app just to pick a track. For short-form video that isn't a nice-to-have, the audio choice is part of the content, so in practice scheduling is unusable for a large share of posts.

What both platforms already expose

Instagram — Meta's Audio API (Content Publishing):

• GET /ig_audio?audio_type=music&user_id=… searches Meta-authorized music; omitting the query returns trending

• Attach to a Reel container with audio_configuration: audio_id, audio_volume (0-100), video_volume (0-100)

• Requires the IG account to be connected via Facebook Login (which Zernio already does)

• Docs: https://developers.facebook.com/docs/instagram-platform/content-publishing/audio-api/

TikTok — Commercial Music Library:

• song_clip_id set on a VIDEO post at creation time (can't be added to a draft afterwards; photo mode doesn't support it)

• Catalog availability depends on the connected account's region and eligibility

Suggested API shape

A search/list endpoint per platform returning audio IDs, plus a field on the existing post payload: audioConfiguration (audioId, audioVolume, videoVolume) on the INSTAGRAM block, songClipId on the TIKTOK block. That would fit the existing createPost structure without a new posting path.

Current state in Zernio

Only audioName (renames the Original Audio label) and autoAddMusic (TikTok photo posts, TikTok picks the track). Confirmed with support that nothing else exists today.