✨ feat(connection-package): 支持导出时多选连接

- 后端导出请求增加 connectionIds，仅打包所选连接
- 导出弹窗支持连接多选与未选校验
- 同步 Wails 绑定与传输测试

frontend/src/utils/connectionExport.ts

@@ -10,6 +10,7 @@ export type ConnectionPackageDialogSnapshot = {
   password: string;
   error: string;
   confirmLoading: boolean;
+  selectedConnectionIds?: string[];
 };
 export type ConnectionPackageDialogUpdater = (
   current: ConnectionPackageDialogSnapshot,