refactor: 整理资源文件，添加legacy路由

- 将原版文件移到frontend/legacy/3dearthmult/
- 纹理文件移到frontend/public/earth/assets/
- vite.config添加/legacy/earth路由支持
- earth.js纹理路径改为assets/

frontend/public/earth/js/earth.js

@@ -28,7 +28,7 @@ export function createEarth(scene) {
   scene.add(earth);
   
   const textureUrls = [
-    './8k_earth_daymap.jpg',
+    './assets/8k_earth_daymap.jpg',
     'https://raw.githubusercontent.com/mrdoob/three.js/dev/examples/textures/planets/earth_atmos_2048.jpg',
     'https://threejs.org/examples/textures/planets/earth_atmos_2048.jpg',
     'https://assets.codepen.io/982762/earth_texture_2048.jpg'

frontend/vite.config.ts

@@ -1,9 +1,43 @@
 import { defineConfig } from 'vite'
 import react from '@vitejs/plugin-react'
 import path from 'path'
+import fs from 'fs'
 
 export default defineConfig({
-  plugins: [react()],
+  plugins: [
+    react(),
+    {
+      name: 'legacy-earth',
+      configureServer(server) {
+        server.middlewares.use('/legacy/earth', (req, res, next) => {
+          let url = req.url || '/'
+          
+          if (url === '' || url === '/') {
+            url = '/3dearthmult.html'
+          }
+          
+          const filePath = path.resolve(__dirname, 'legacy/3dearthmult' + url)
+          
+          if (fs.existsSync(filePath) && fs.statSync(filePath).isFile()) {
+            const ext = path.extname(filePath).toLowerCase()
+            const contentTypes = {
+              '.html': 'text/html',
+              '.json': 'application/json',
+              '.jpg': 'image/jpeg',
+              '.jpeg': 'image/jpeg',
+              '.png': 'image/png',
+              '.js': 'application/javascript',
+              '.css': 'text/css'
+            }
+            res.setHeader('Content-Type', contentTypes[ext] || 'text/plain')
+            fs.createReadStream(filePath).pipe(res)
+          } else {
+            next()
+          }
+        })
+      }
+    }
+  ],
   server: {
     port: 3000,
     proxy: {