refactor: import setupLayouts from virtual module (#125)

As shown in the vite-plugin-vue readme

src/main.ts

@@ -1,6 +1,6 @@
 import { ViteSSG } from 'vite-ssg'
 import generatedRoutes from 'virtual:generated-pages'
-import { setupLayouts } from 'layouts-generated'
+import { setupLayouts } from 'virtual:generated-layouts'
 import App from './App.vue'
 import 'virtual:windi.css'
 import 'virtual:windi-devtools'