refactor: 提取地球坐标常量到EARTH_CONFIG

- 添加tilt、chinaLat、chinaLon、latCoefficient等常量
- earth.js和controls.js使用常量替代硬编码
- 离开地球时隐藏tooltip

frontend/public/earth/js/constants.js

@@ -9,6 +9,20 @@ export const CONFIG = {
   rotationSpeed: 0.002,
 };
 
+// Earth coordinate constants
+export const EARTH_CONFIG = {
+  tilt: 23.5,  // earth tilt angle (degrees)
+  tiltRad: 23.5 * Math.PI / 180,  // earth tilt angle (radians)
+  
+  // hangzhou coordinates
+  chinaLat: 30.2741,
+  chinaLon: 120.1552,
+  chinaRotLon: 120.1552 - 270,  // for rotation calculation (chinaLon - 270)
+  
+  // view reset coefficient
+  latCoefficient: 0.5
+};
+
 export const PATHS = {
   cablesApi: '/api/v1/visualization/geo/cables',
   landingPointsApi: '/api/v1/visualization/geo/landing-points',