Custom 404/Error page (#133)

* feat(frontend): custom 404 + error page with intl formatting

* style(frontend): add styling for error message

src/pages/404.tsx

@@ -0,0 +1,39 @@
+import Link from 'next/link';
+import React from 'react';
+import { defineMessages, FormattedMessage } from 'react-intl';
+
+const messages = defineMessages({
+  pageNotFound: '404 - Page Not Found',
+  returnHome: 'Return Home',
+});
+
+const Custom404: React.FC = () => {
+  return (
+    <div className="error-message">
+      <div className="text-4xl">
+        <FormattedMessage {...messages.pageNotFound} />
+      </div>
+      <Link href="/">
+        <a className="flex">
+          <FormattedMessage {...messages.returnHome} />
+          <svg
+            className="w-6 h-6 ml-2"
+            fill="none"
+            stroke="currentColor"
+            viewBox="0 0 24 24"
+            xmlns="http://www.w3.org/2000/svg"
+          >
+            <path
+              strokeLinecap="round"
+              strokeLinejoin="round"
+              strokeWidth={2}
+              d="M13 9l3 3m0 0l-3 3m3-3H8m13 0a9 9 0 11-18 0 9 9 0 0118 0z"
+            />
+          </svg>
+        </a>
+      </Link>
+    </div>
+  );
+};
+
+export default Custom404;