feat: use unhead v2 (#549)

Co-authored-by: Anthony Fu <github@antfu.me>

src/layouts/404.vue

@@ -1,6 +1,9 @@
 <script setup lang="ts">
 const router = useRouter()
 const { t } = useI18n()
+useHead({
+  title: () => t('not-found'),
+})
 </script>
 
 <template>