- Add ChannelType.WEB = 'web' to shared/models/message.py
- Add webchat_response_key() to shared/redis_keys.py
- Create WebConversation and WebConversationMessage ORM models (SQLAlchemy 2.0)
- Create migration 008_web_chat.py with RLS, indexes, and channel_type CHECK update
- Pop conversation_id/portal_user_id extras in handle_message before model_validate
- Add web case to _build_response_extras and _send_response (Redis pub-sub publish)
- Import webchat_response_key in orchestrator/tasks.py
- Write 19 unit tests covering CHAT-01 through CHAT-05 (all pass)
- Add MediaType(StrEnum) and MediaAttachment(BaseModel) to shared/models/message.py
- Add media: list[MediaAttachment] field to MessageContent
- Add whatsapp_app_secret, whatsapp_verify_token, and MinIO settings to shared/config.py
- Add normalize_whatsapp_event() to gateway/normalize.py (text, image, document support)
- Create whatsapp.py adapter with verify_whatsapp_signature() and verify_hub_challenge()
- 30 new passing tests (signature verification + normalizer)