feat(frontend): 404 redirection (#2309)

# Description

Please include a summary of the changes and the related issue. Please
also include relevant motivation and context.

## Checklist before requesting a review

Please delete options that are not relevant.

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented hard-to-understand areas
- [ ] I have ideally added tests that prove my fix is effective or that
my feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged

## Screenshots (if appropriate):

frontend/app/not-found.tsx

@@ -0,0 +1,14 @@
+import Link from "next/link";
+
+const NotFound = (): JSX.Element => {
+  return (
+    <div>
+      <h1>Not found – 404!</h1>
+      <div>
+        <Link href="/">Go back to Home</Link>
+      </div>
+    </div>
+  );
+};
+
+export default NotFound;