Implement WebSocket Real-Time Notifications

Build a real-time notification system using WebSockets. The implementation should include:

**Server:**
- WebSocket server setup with connection authentication (verify JWT on upgrade)
- Room/channel management for per-user and per-topic subscriptions
- Heartbeat mechanism with configurable ping/pong interval
- Graceful reconnection handling with message buffering
- Message types: notification, typing_indicator, presence_update, data_sync
- Redis pub/sub for horizontal scaling across multiple server instances

**Client:**
- React hook: useWebSocket with auto-reconnect and exponential backoff
- Connection state management (connecting, connected, disconnected, error)
- Message queue for offline resilience
- Notification toast component with dismiss, action buttons, and stacking
- Unread count badge component

**Shared:**
- TypeScript message type definitions
- Protocol version negotiation
- Message serialization/deserialization