fix(satellites): prevent selecting satellites on far side of earth

- Add isSatelliteFrontFacing() to detect if satellite is on visible side
- Filter satellites in hover and click handlers by front-facing check
- Apply same logic as cables for consistent back-face culling

frontend/public/earth/js/satellites.js

@@ -415,6 +415,20 @@ export function getSatellitePositions() {
   return satellitePositions;
 }
 
+export function isSatelliteFrontFacing(index, camera) {
+  if (!earthObjRef || !camera) return true;
+  const positions = satellitePositions;
+  if (!positions || !positions[index]) return true;
+  
+  const satPos = positions[index].current;
+  if (!satPos) return true;
+  
+  const toCamera = new THREE.Vector3().subVectors(camera.position, earthObjRef.position).normalize();
+  const toSat = new THREE.Vector3().subVectors(satPos, earthObjRef.position).normalize();
+  
+  return toCamera.dot(toSat) < 0;
+}
+
 let earthObjRef = null;
 let sceneRef = null;