fix: menu.ui is now a Menu widget, not a plain JSON list

wwwroot/menu.ui

@@ -1,4 +1,8 @@
-[
+{
+    "widgettype": "Menu",
+    "id": "contract_menu",
+    "options": {
+        "items": [
             {
                 "name": "contracts",
                 "label": "合同列表",
@@ -19,4 +23,6 @@
                 "label": "AI配置",
                 "url": "{{entire_url('ai_config.ui')}}"
             }
-]
+        ]
+    }
+}