Add a new channel plugin for Zoom Team Chat integration:
- Server-to-Server OAuth with client_credentials grant
- Webhook signature verification (HMAC-SHA256)
- Support for both DMs and channel messages
- Policy controls for DMs and group messaging
- Onboarding wizard for credentials setup
- Connection health probe
Requires a Zoom Team Chat app with `imchat:bot` scope.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
