Add NotFoundPage component to handle 404 errors

app/not-found.tsx

@@ -0,0 +1,20 @@
+import { Button } from "@/components/ui/button";
+import Link from "next/link";
+
+function NotFoundPage() {
+  return (
+    <div className="grid h-screen place-content-center px-4">
+      <div className="text-center">
+        <h1 className="text-9xl font-black">404</h1>
+        <p className="text-2xl font-bold tracking-tight sm:text-4xl">Uh-oh!</p>
+        <p className="mt-4 text-gray-500">We can't find that page.</p>
+
+        <Button asChild className="mt-6 text-foreground">
+          <Link href="/">Go Back Home</Link>
+        </Button>
+      </div>
+    </div>
+  );
+}
+
+export default NotFoundPage;