- Updated the WebSocket hub to replace the insecure `user_id` query parameter with an authentication token for secure connections.
- Introduced typed events for mail operations (created, updated, deleted) to streamline event handling.
- Implemented heartbeat functionality (ping/pong) to maintain connection health.
- Enhanced client reconnection logic and delta replay for improved user experience.
- Added limits on connections per user/session to prevent abuse and ensure stability.
