feat(desktop-client): 阶段4-6 Electron EXE 客户端（登录/课表/作业/通知/成绩/设置 + Socket.IO 实时 + IndexedDB 离线缓存与自动同步 + electron-builder 打包）

packages/desktop-client/scripts/build-main.mjs

@@ -0,0 +1,37 @@
+/**
+ * 主进程 / preload 构建：esbuild 打包为 CommonJS。
+ * - external: electron（由 Electron 运行时提供）
+ * - @classhelper/shared 会被内联打包（ESM 源码 -> CJS 产物）
+ */
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { build } from 'esbuild';
+
+const root = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..');
+
+const shared = {
+  bundle: true,
+  platform: 'node',
+  target: 'node20',
+  format: 'cjs',
+  sourcemap: false,
+  external: ['electron'],
+  logLevel: 'warning',
+  define: {
+    'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV ?? 'production'),
+  },
+};
+
+await build({
+  ...shared,
+  entryPoints: [path.join(root, 'src/main/index.ts')],
+  outfile: path.join(root, 'dist/main/index.js'),
+});
+
+await build({
+  ...shared,
+  entryPoints: [path.join(root, 'src/preload/index.ts')],
+  outfile: path.join(root, 'dist/preload/index.js'),
+});
+
+console.log('[build:main] dist/main/index.js 与 dist/preload/index.js 构建完成');