feat: use the not-found component instead of the invalid route component in the backend mode

* 后端菜单模式下，使用not-found组件代替无效的路由组件

Author: mynetfan

packages/utils/src/helpers/generate-routes-backend.ts

@@ -63,6 +63,7 @@ function convertRoutes(
         route.component = pageMap[pageKey];
       } else {
         console.error(`route component is invalid: ${pageKey}`, route);
+        route.component = pageMap['/_core/fallback/not-found.vue'];
       }
     }