Backend: UTC nel DB, +00:00 nelle API, ora italiana solo in presentazione (#42)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/backend/api/middleware/api_key.py

@@ -9,7 +9,8 @@ from src.backend.database import get_db
 from src.backend.config import settings
 from src.backend.models.orm.api_key import ApiKey
 from src.backend.models.orm.user import User
-from src.backend.services.auth_service import hash_api_key, utcnow
+from src.backend.services.auth_service import hash_api_key
+from src.backend.utils.tempo import utcnow
 
 _RENEW_INTERVAL = timedelta(minutes=5)