Add a more usable 404 page

Author: nghtctrl

src/pages/404.astro

@@ -0,0 +1,29 @@
+---
+import Layout from '../layouts/Layout.astro';
+import Link from '../components/Link.astro';
+
+const metadata = {
+  title: 'Page Not Found',
+  useTitleTemplate: true,
+  index: false,
+};
+---
+
+<Layout metadata={metadata}>
+  <h1>404 &mdash; Page Not Found</h1>
+  <p>
+    This page may have been moved, renamed, removed, or doesn't exist. If an AI
+    chatbot or search engine summary brought you here, it may have hallucinated
+    a nonexistent page.
+  </p>
+  <p>Here's what you can do:</p>
+  <ul>
+    <li>Click your browser's back button to return to the previous page.</li>
+    <li>Browse the menu above to find what you're looking for.</li>
+    <li>
+      Send the link to <Link url='mailto:support@jihokim.com'
+        >support@jihokim.com</Link
+      >, and I might be able to tell you why it is broken.
+    </li>
+  </ul>
+</Layout>