Task 10.3: Notification Service (WebSocket) Implementation

[kluth]

Phase: 10 - Showcase Application (Lower Priority)

Tags: feature, showcase, websocket

Description:
Implement WebSocket server, add EventBus subscriptions, broadcast logic, connection rate limiting, and write WebSocket tests.

Acceptance Criteria:

• Implement WebSocket server
• Add EventBus subscriptions
• Implement broadcast logic
• Add connection rate limiting
• Write WebSocket tests