- Add WhatsApp channel module with Cloud API v18.0 support
- Implement webhook-based message reception and API sending
- Add allowlist for phone numbers (E.164 format or wildcard)
- Add WhatsApp webhook endpoints to gateway (/whatsapp GET/POST)
- Add WhatsApp config schema with TOML support
- Wire WhatsApp into channel factory, CLI, and doctor commands
- Add WhatsApp to setup wizard with connection testing
- Add comprehensive test coverage (47 channel tests + 9 URL decoding tests)
- Update README with detailed WhatsApp setup instructions
- Support text messages only, skip media/status updates
- Normalize phone numbers with + prefix
- Handle webhook verification with Meta challenge-response
All 756 tests pass. Ready for production use.
