Fix/custom 404 page

frontend/src/app/not-found.tsx

@@ -0,0 +1,24 @@
+import Link from "next/link";
+import { Button } from "@/components/ui/button";
+import { GoBackButton } from "@/components/GoBackButton";
+
+export default function NotFound() {
+  return (
+    <div className="flex min-h-screen flex-col items-center justify-center gap-6 px-4 text-center">
+      <h1 className="text-6xl font-bold tracking-tight">404</h1>
+      <h2 className="text-2xl font-semibold">Page Not Found</h2>
+      <p className="max-w-md text-muted-foreground">
+        The page you&apos;re looking for doesn&apos;t exist or may have been moved.
+      </p>
+
+      <div className="flex flex-wrap items-center justify-center gap-3">
+        <Link href="/">
+          <Button>Return to Home</Button>
+        </Link>
+        <Link href="/dashboard">
+        </Link>
+        <GoBackButton />
+      </div>
+    </div>
+  );
+}

frontend/src/components/GoBackButton.tsx

@@ -0,0 +1,11 @@
+"use client";
+
+import { Button } from "@/components/ui/button";
+
+export function GoBackButton() {
+  return (
+    <Button variant="outline" onClick={() => window.history.back()}>
+      Go Back
+    </Button>
+  );
+}