fix(config): add individual menu CRUD endpoints and fix frontend menu data handling

- Add POST /config/menus (create single menu)
- Add PUT /config/menus/{id} (update single menu)
- Add DELETE /config/menus/{id} (soft delete single menu)
- Frontend MenuConfig was calling individual CRUD routes that didn't exist,
  causing 404 errors on all create/update/delete operations
- Fix frontend to correctly handle nested tree response from backend

apps/web/src/pages/settings/MenuConfig.tsx

@@ -35,6 +35,20 @@ interface MenuItem {
 
 // --- Helpers ---
 
+/** Convert nested menu tree back to flat list */
+function flattenMenuTree(tree: MenuItem[]): MenuItem[] {
+  const result: MenuItem[] = [];
+  const walk = (items: MenuItem[]) => {
+    for (const item of items) {
+      const { children, ...rest } = item;
+      result.push(rest as MenuItem);
+      if (children?.length) walk(children);
+    }
+  };
+  walk(tree);
+  return result;
+}
+
 /** Convert flat menu list to tree structure for Table children prop */
 function buildMenuTree(items: MenuItem[]): MenuItem[] {
   const map = new Map<string, MenuItem>();
@@ -92,9 +106,10 @@ export default function MenuConfig() {
     setLoading(true);
     try {
       const { data: resp } = await client.get('/config/menus');
-      const list: MenuItem[] = resp.data ?? resp;
-      setMenus(list);
-      setMenuTree(buildMenuTree(list));
+      // 后端返回嵌套树结构，直接使用
+      const tree: MenuItem[] = resp.data ?? resp;
+      setMenus(flattenMenuTree(tree));
+      setMenuTree(tree);
     } catch {
       message.error('加载菜单失败');
     }