Add music option in dashboard/API

This works today through the API for Instagram Reels, and it shipped on 10 August 2026. Search the catalog with GET /v1/accounts/{accountId}/instagram/audio (trending, or q to search, plus GET /v1/accounts/{accountId}/instagram/audio/{audioId} for lookup), then attach the track by sending platformSpecificData.audioConfiguration (audioId, optional audioVolume and videoVolume) on the Reel in POST /v1/posts. Two limits come from Meta rather than from us: the audio catalog endpoint only exists for Instagram accounts connected via Facebook Login, and no other platform's publishing API accepts music (TikTok's Content Posting API in particular requires the sound to be added inside the app after posting). This is API-only by design, there is no music picker in the dashboard.