feat: introduce layouts (#28)

layouts/404.vue

@@ -0,0 +1,18 @@
+<script setup lang="ts">
+const router = useRouter()
+</script>
+
+<template>
+  <main p="x4 y10" text="center teal-700 dark:gray-200">
+    <div text-4xl>
+      <div i-carbon-warning inline-block />
+    </div>
+    <slot />
+    <div>
+      <button btn text-sm m="3 t8" @click="router.back()">
+        Back
+      </button>
+    </div>
+    <Footer />
+  </main>
+</template>