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-simple.cjs

@@ -0,0 +1,17 @@
+const { contextBridge, ipcRenderer } = require('electron');
+
+// 暴露简化的 API 给渲染进程
+contextBridge.exposeInMainWorld('electronAPI', {
+    // 获取应用版本
+    getAppVersion: () => ipcRenderer.invoke('get-app-version'),
+    
+    // 获取平台信息
+    getPlatform: () => ipcRenderer.invoke('get-platform'),
+    
+    // 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;