feat: 404 page emitter

quartz/components/pages/404.tsx

@@ -0,0 +1,12 @@
+import { QuartzComponentConstructor } from "../types"
+
+function NotFound() {
+  return (
+    <article class="popover-hint">
+      <h1>404</h1>
+      <p>Either this page is private or doesn't exist.</p>
+    </article>
+  )
+}
+
+export default (() => NotFound) satisfies QuartzComponentConstructor