feat: add 404 page

pages/404.vue

@@ -0,0 +1,13 @@
+<script setup lang="ts">
+useTitle("404 - Not Found", "You're lost!");
+</script>
+
+<template>
+  <main class="prose dark:prose-invert max-w-3xl transition">
+    <h1 class="mb-1">404 - Not Found</h1>
+    <p>
+      You're lost! Don't worry, here's a link
+      <a href="/">back to the home page.</a>
+    </p>
+  </main>
+</template>