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/controls.js

@@ -1,6 +1,6 @@
 // controls.js - Zoom, rotate and toggle controls
 
-import { CONFIG } from './constants.js';
+import { CONFIG, EARTH_CONFIG } from './constants.js';
 import { updateZoomDisplay, showStatusMessage } from './ui.js';
 import { toggleTerrain } from './earth.js';
 import { reloadData } from './main.js';
@@ -153,13 +153,9 @@ function animateValue(start, end, duration, onUpdate, onComplete) {
 export function resetView(camera) {
   if (!earthObj) return;
   
-  const chinaLat = 40;
-  const chinaLon = -154;
-  
-  const baseTilt = 23.5 * Math.PI / 180;
-  const latRot = chinaLat * Math.PI / 180;
-  const targetRotX = baseTilt + latRot * 0.5;
-  const targetRotY = -(chinaLon * Math.PI / 180);
+  const latRot = EARTH_CONFIG.chinaLat * Math.PI / 180;
+  const targetRotX = EARTH_CONFIG.tiltRad + latRot * EARTH_CONFIG.latCoefficient;
+  const targetRotY = -(EARTH_CONFIG.chinaRotLon * Math.PI / 180);
   
   const startRotX = earthObj.rotation.x;
   const startRotY = earthObj.rotation.y;
@@ -176,7 +172,7 @@ export function resetView(camera) {
     updateZoomDisplay(zoomLevel, camera.position.z.toFixed(0));
   }, () => {
     zoomLevel = 1.0;
-    showStatusMessage('视角已重置到中国', 'info');
+    showStatusMessage('视角已重置', 'info');
   });
   
   if (typeof window.clearLockedCable === 'function') {