feat(earth): add predicted orbit display for locked satellites

- Calculate orbital period from meanMotion
- Generate predicted orbit points with 10s sampling
- Show complete orbit line when satellite is locked
- Hide orbit when satellite is unlocked
- Color gradient: bright (current) to dark (end)
- Fix TLE epoch format issue with fallback circle orbit
- Add visibility change handler to clear trails on page hide
- Fix satellite count display after loading
- Merge predicted-orbit plan into single file

frontend/public/earth/js/constants.js

@@ -60,6 +60,11 @@ export const SATELLITE_CONFIG = {
   apiPath: '/api/v1/visualization/geo/satellites'
 };
 
+export const PREDICTED_ORBIT_CONFIG = {
+  sampleInterval: 10,
+  opacity: 0.8
+};
+
 export const GRID_CONFIG = {
   latitudeStep: 10,
   longitudeStep: 30,