feat(tasks): T55-T58 implement background tasks for OpenRouter sync

- T55: Setup APScheduler with AsyncIOScheduler and @scheduled_job decorator
- T56: Implement hourly usage stats sync from OpenRouter API
- T57: Implement daily API key validation job
- T58: Implement weekly cleanup job for old usage stats
- Add usage_stats_retention_days config option
- Integrate scheduler with FastAPI lifespan events
- Add 26 unit tests for scheduler, sync, and cleanup tasks
- Add apscheduler to requirements.txt

The background tasks now automatically:
- Sync usage stats every hour from OpenRouter
- Validate API keys daily at 2 AM UTC
- Clean up old data weekly on Sunday at 3 AM UTC

docker-compose.yml

@@ -0,0 +1,60 @@
+version: '3.8'
+
+services:
+  app:
+    build:
+      context: .
+      dockerfile: Dockerfile
+    container_name: openrouter-watcher
+    restart: unless-stopped
+    ports:
+      - "8000:8000"
+    environment:
+      - DATABASE_URL=sqlite:///./data/app.db
+      - SECRET_KEY=${SECRET_KEY:-change-this-secret-key-in-production}
+      - ENCRYPTION_KEY=${ENCRYPTION_KEY:-change-this-encryption-key-in-prod}
+      - OPENROUTER_API_URL=https://openrouter.ai/api/v1
+      - MAX_API_KEYS_PER_USER=10
+      - MAX_API_TOKENS_PER_USER=5
+      - RATE_LIMIT_REQUESTS=100
+      - RATE_LIMIT_WINDOW=3600
+      - JWT_EXPIRATION_HOURS=24
+      - DEBUG=false
+      - LOG_LEVEL=INFO
+    volumes:
+      - ./data:/app/data
+      - ./logs:/app/logs
+    networks:
+      - openrouter-network
+    healthcheck:
+      test: ["CMD", "curl", "-f", "http://localhost:8000/health"]
+      interval: 30s
+      timeout: 10s
+      retries: 3
+      start_period: 40s
+
+  # Servizio opzionale per backup automatico (commentato)
+  # backup:
+  #   image: busybox
+  #   container_name: openrouter-backup
+  #   volumes:
+  #     - ./data:/data:ro
+  #     - ./backups:/backups
+  #   command: >
+  #     sh -c "while true; do
+  #       sleep 86400 &&
+  #       cp /data/app.db /backups/app-$$(date +%Y%m%d).db
+  #     done"
+  #   restart: unless-stopped
+  #   networks:
+  #     - openrouter-network
+
+networks:
+  openrouter-network:
+    driver: bridge
+
+volumes:
+  data:
+    driver: local
+  logs:
+    driver: local