添加 GitHub Actions Windows 构建流程

- 新增 .github/workflows/build-windows.yml，在 windows-latest runner 上构建 NSIS 安装包
- 修复 PYTHON_BIN 在 Windows 下需要 .exe 后缀
- 更新 extraResources 为目录式 glob，同时兼容 macOS (main) 和 Windows (main.exe)
- package.json 新增 win/nsis electron-builder 目标配置

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

electron/ipc/templateIpc.js

@@ -8,7 +8,11 @@ const APPDATA_DIR = path.join(app.getPath("userData"), "excel-batch-editor", "te
 fs.mkdirSync(APPDATA_DIR, { recursive: true });
 
 const PYTHON_BIN = app.isPackaged
-  ? path.join(process.resourcesPath, "python", "main")
+  ? path.join(
+      process.resourcesPath,
+      "python",
+      process.platform === "win32" ? "main.exe" : "main"
+    )
   : path.join(__dirname, "../../python/main.py");
 
 function callPython(payload) {