refactor: 确立独立子工程架构 (backend, admin, mpuniapp) 并同步更新 AGENTS.md 规范

admin/src/utils/changeTheme.ts

@@ -0,0 +1,9 @@
+function changeTheme(theme) {
+  if (theme === 'dark') {
+    document.body.setAttribute('arco-theme', 'dark');
+  } else {
+    document.body.removeAttribute('arco-theme');
+  }
+}
+
+export default changeTheme;