Fix CI issues: update Cesium, add package-lock.json, fix linting

- Removed non-existent @cesium/engine package
- Updated cesium to ^1.123.0
- Added package-lock.json for reproducible builds
- Fixed unused import in orbit_propagator.py

Author: amychenn

backend/core-orbits/app/services/orbit_propagator.py

@@ -11,7 +11,7 @@
 at any given time.
 """
 from datetime import datetime, timezone
-from typing import Dict, Any, Optional, Tuple
+from typing import Dict, Any, Tuple
 import math
 
 from sgp4.api import Satrec, jday
@@ -187,7 +187,7 @@ def _eci_to_geodetic(
             Tuple of (latitude_deg, longitude_deg, altitude_km)
         """
         # Earth rotation rate (rad/s)
-        omega_earth = 7.2921150e-5
+        _omega_earth = 7.2921150e-5  # noqa: F841 - kept for documentation
 
         # Calculate Greenwich Mean Sidereal Time (GMST)
         # This is a simplified calculation