add basic frontend

frontend/src/routes/notfound/index.tsx

@@ -0,0 +1,17 @@
+import { FunctionalComponent, h } from 'preact';
+import { Link } from 'preact-router/match';
+import style from './style.css';
+
+const Notfound: FunctionalComponent = () => {
+    return (
+        <div class={style.notfound}>
+            <h1>Error 404</h1>
+            <p>That page doesn&apos;t exist.</p>
+            <Link href="/">
+                <h4>Back to Home</h4>
+            </Link>
+        </div>
+    );
+};
+
+export default Notfound;