Refresh one account now instead of waiting for the nightly pass

Reads the platform inside the request, writes the snapshots, then returns the refreshed analytics. Covers up to the 1000 most recent posts.

This is a write: it rotates OAuth tokens, stores snapshots and consumes the platform's rate limit, so it needs manage access to the account, not read access. Use it when someone has just published from the platform's own app — the collector otherwise runs once a night.