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

admin/.prettierrc

@@ -0,0 +1,7 @@
+{
+  "semi": true,
+  "singleQuote": true,
+  "jsxSingleQuote": false,
+  "useTabs": false,
+  "tabWidth": 2
+}