feat: add NotFound component to handle 404 errors and redirect unauthenticated users

app/not-found.tsx

@@ -0,0 +1,33 @@
+"use client";
+
+import { useEffect } from "react";
+import { useAuthStore } from "@/stores/auth-store";
+
+export default function NotFound() {
+  const isAuthenticated = useAuthStore((s) => s.isAuthenticated);
+
+  useEffect(() => {
+    if (!isAuthenticated) {
+      window.location.href = "/login";
+    }
+  }, [isAuthenticated]);
+
+  if (!isAuthenticated) {
+    return null;
+  }
+
+  return (
+    <div className="min-h-screen flex items-center justify-center bg-background">
+      <div className="text-center max-w-md px-4">
+        <h1 className="text-4xl font-bold text-foreground mb-2">404</h1>
+        <p className="text-muted-foreground mb-6">This page could not be found.</p>
+        <a
+          href="/"
+          className="inline-flex items-center px-4 py-2 bg-primary text-primary-foreground rounded-lg hover:opacity-90 transition-opacity"
+        >
+          Go home
+        </a>
+      </div>
+    </div>
+  );
+}