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/earth.js

@@ -1,7 +1,7 @@
 // earth.js - 3D Earth creation module
 
 import * as THREE from 'three';
-import { CONFIG } from './constants.js';
+import { CONFIG, EARTH_CONFIG } from './constants.js';
 import { latLonToVector3 } from './utils.js';
 
 export let earth = null;
@@ -22,9 +22,9 @@ export function createEarth(scene) {
     opacity: 0.8,
     side: THREE.DoubleSide
   });
-  
+   
   earth = new THREE.Mesh(geometry, material);
-  earth.rotation.x = 23.5 * Math.PI / 180;
+  earth.rotation.x = EARTH_CONFIG.tiltRad;
   scene.add(earth);
   
   const textureUrls = [