feat(08-01): Health monitoring & logging infrastructure

- Set up Winston structured logging with console and file outputs
- Create GET /api/health endpoint with uptime, database status, response times
- Add request logging middleware (method, path, statusCode, duration)
- Create health monitoring module with database connectivity checks
- Log all HTTP requests with timing information
- Log auth events (login, register) and data modifications
- Replace console.log/error with structured logger calls
- Update backend README with logging configuration documentation
- Add tests for health endpoint and logging middleware
- Logs directory: logs/combined.log and logs/error.log

Deliverables met:
✓ Structured logging (Winston) integrated
✓ Enhanced health endpoint with uptime & database info
✓ Request logging middleware attached to all routes
✓ Comprehensive logging documentation in README.md
✓ Tests passing for health and logging functionality
✓ All critical operations logged with context

backend/package.json

@@ -13,7 +13,8 @@
     "cors": "^2.8.5",
     "express": "^4.18.2",
     "jsonwebtoken": "^9.0.2",
-    "pg": "^8.11.3"
+    "pg": "^8.11.3",
+    "winston": "^3.19.0"
   },
   "devDependencies": {
     "nodemon": "^3.0.2",