Convert web app to Electron desktop application

- Add Electron main process with developer tools support
- Create preload script for secure context bridge
- Configure electron-builder for packaging
- Update Vite config for Electron compatibility (base: './')
- Add environment variable support for API host configuration
- Fix i18n to use relative paths for Electron file protocol
- Restore multi-port backend architecture (8081-8085)
- Add enhanced backend startup script with port checking
- Update package.json with Electron dependencies and build scripts

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

electron/preload.cjs

@@ -0,0 +1,54 @@
+const { contextBridge, ipcRenderer } = require('electron');
+
+// 暴露安全的 API 给渲染进程
+contextBridge.exposeInMainWorld('electronAPI', {
+    // 获取后端端口
+    getBackendPort: () => ipcRenderer.invoke('get-backend-port'),
+    
+    // 获取应用版本
+    getAppVersion: () => ipcRenderer.invoke('get-app-version'),
+    
+    // 获取平台信息
+    getPlatform: () => ipcRenderer.invoke('get-platform'),
+    
+    // 重启后端
+    restartBackend: () => ipcRenderer.invoke('restart-backend'),
+    
+    // 文件对话框
+    showSaveDialog: (options) => ipcRenderer.invoke('show-save-dialog', options),
+    showOpenDialog: (options) => ipcRenderer.invoke('show-open-dialog', options),
+    
+    // 监听后端事件
+    onBackendStarted: (callback) => {
+        ipcRenderer.on('backend-started', (event, data) => callback(data));
+    },
+    
+    onBackendLog: (callback) => {
+        ipcRenderer.on('backend-log', (event, data) => callback(data));
+    },
+    
+    onBackendError: (callback) => {
+        ipcRenderer.on('backend-error', (event, data) => callback(data));
+    },
+    
+    // 监听更新事件
+    onUpdateAvailable: (callback) => {
+        ipcRenderer.on('update-available', () => callback());
+    },
+    
+    onUpdateDownloaded: (callback) => {
+        ipcRenderer.on('update-downloaded', () => callback());
+    },
+    
+    // 移除事件监听器
+    removeAllListeners: (channel) => {
+        ipcRenderer.removeAllListeners(channel);
+    },
+    
+    // 环境检测
+    isElectron: true,
+    isDev: process.env.NODE_ENV === 'development',
+});
+
+// 添加一个标识，让渲染进程知道这是 Electron 环境
+window.IS_ELECTRON = true;