Get System Broadcast Recipients

How many people a WhatsApp notification would actually reach.

{"active_users": int, "with_whatsapp": int, "window_days": 30}

"Active" is Z_Users.last_seen_at — stamped by app/auth.py on every authenticated request (debounced to once per 10 minutes per user) and already the system's answer to "is this person still using StandGest", per the inactive-user lifecycle cron. There is no last-login column and no sessions table; see app/db/system_broadcasts.py::list_active_user_contacts.

with_whatsapp counts REACHABLE numbers, not stored ones: it runs the same to_e164 + mobile check the send does, so the number shown before pressing Enviar is the number that gets queued. Read-only, and degrades to zeros rather than erroring — a count that cannot be produced must not block the announcement.