Implement Real-Time Notifications (WebSocket Gateway)

[phertyameen]

Set up a WebSocket gateway for real-time updates (job status, escrow payments, messages).

Tasks:

Create NotificationGateway using @WebSocketGateway.

Emit events:

gigCreated

paymentReleased

messageReceived

Integrate with Redis Pub/Sub to scale horizontally.

Ensure JWT-authenticated sockets.

Acceptance Criteria:

✅ Clients/freelancers receive real-time updates when events occur.

✅ WebSocket is secure (only logged-in users can subscribe).

✅ Notifications are consistent across multiple server instances.