webapp: use modern component format

webapp/src/App.vue

@@ -6,14 +6,15 @@
 </template>
 
 <script lang="ts">
+import { defineComponent } from 'vue';
 import NavBar from "./components/NavBar.vue";
 
-export default {
+export default defineComponent({
     name: "App",
     components: {
         NavBar,
     },
-};
+});
 </script>
 
 <style>