chore(docs): update save and restore example

docs/examples/save-restore/App.vue

@@ -1,13 +1,18 @@
-<script lang="ts" setup>
+<script setup>
 import { ref } from 'vue'
 import { VueFlow } from '@vue-flow/core'
+import { Background } from '@vue-flow/background'
 import SaveRestoreControls from './Controls.vue'
 
 const nodes = ref([{ id: '1', label: 'Node 1', position: { x: 100, y: 100 } }])
+
+const edges = ref([])
 </script>
 
 <template>
-  <VueFlow :nodes="nodes">
+  <VueFlow :nodes="nodes" :edges="edges">
     <SaveRestoreControls />
+
+    <Background />
   </VueFlow>
 </template>