feat: Implement Step 10-11 - Statistics and Notification Services

Step 10: Data Analytics and Statistics Service
- Created comprehensive statistics service with real-time metrics collection
- Implemented time-series data storage interface (InfluxDB compatible)
- Added data aggregation and analytics endpoints
- Integrated Redis caching for performance optimization
- Made Kafka connection optional for resilience

Step 11: Real-time Notification System
- Built multi-channel notification service (Email, SMS, Push, In-App)
- Implemented priority-based queue management with Redis
- Created template engine for dynamic notifications
- Added user preference management for personalized notifications
- Integrated WebSocket server for real-time updates
- Fixed pymongo/motor compatibility issues (motor 3.5.1)

Testing:
- Created comprehensive test suites for both services
- Added integration test script to verify cross-service communication
- All services passing health checks and functional tests

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

services/notifications/backend/requirements.txt

@@ -0,0 +1,11 @@
+fastapi==0.109.0
+uvicorn[standard]==0.27.0
+pydantic==2.5.3
+python-dotenv==1.0.0
+redis==5.0.1
+motor==3.5.1
+pymongo==4.6.1
+httpx==0.26.0
+websockets==12.0
+aiofiles==23.2.1
+python-multipart==0.0.6