v9.21.0 — Instagram channel Cloud Functions

New opt-in firebase/functions-instagram/ codebase (caspian-instagram): Facebook-Login OAuth exchange, feed read, and comment moderation (reply/hide/delete) for the Caspian POS, plus a daily token refresh. Meta Graph v21 over global fetch; META_APP_ID/META_APP_SECRET via defineSecret; the instagram/connection token doc is server-only. New --with-instagram scaffolder flag (mirrors --with-stripe/--with-email). Backports the backend already shipped in luivante/husnella so the library stays a superset. No consumer action required — purely additive.