add custom 404 page

app/not-found.tsx

@@ -0,0 +1,17 @@
+'use client';
+
+import { useRouter } from 'next/navigation';
+import Button from './components/Button';
+
+export default function Custom404() {
+  const router = useRouter();
+  return (
+    <div className="h-[80vh] w-full flex flex-col gap-5 items-center justify-center">
+      <h1 className="text-6xl font-semibold">404</h1>
+      <h2 className="text-3xl text-neutral-500 pb-10">{`Oops! This page doesn't exist`}</h2>
+      <div className="w-[250px]">
+        <Button label="Go to Homepage" onClick={() => router.push('/')} small />
+      </div>
+    </div>
+  );
+}