merge: integrate origin/main squash; keep expanded seed and Facebook connection fix

feat: expand seed to 28 countries/66 states/132 cities; fix Facebook double-message ConnectTimeout

feat: backend completo — FastAPI, MongoDB, webhook Facebook, seeder

feat: send llave in two separate messages for easy copy-paste

fix: trigger always restarts flow; remove MSG_PROCESSING to avoid double API call

fix: filter Facebook echo messages in webhook

fix: use explicit PAGE_ID in Messenger endpoint, add FB_PAGE_ID setting

fix: correct indentation of except block in facebook.py (SyntaxError)

fix: revert facebook.py to httpx (requests+to_thread caused ReadTimeout)

fix: switch Facebook API calls to requests+asyncio.to_thread for proxy/network compat

feat: add seed service, admin router and seed endpoint

fix: respond 200 immediately via BackgroundTasks, add message dedup, reduce retries to 2

fix: webhook error handling, retry logic, processing feedback, bcrypt compat

feat: implement complete FastAPI backend with MongoDB, JWT auth, Facebook webhook

Initial commit