fix(nav): fix exam flow navigation

chore(zustand): refactor auth code for zustand store

components/ExamGuard.tsx

@@ -0,0 +1,25 @@
+"use client";
+
+import { useNavStore } from "@/stores/navStore";
+import { useRouter, usePathname } from "next/navigation";
+import { useEffect } from "react";
+
+export function ExamGuard({ children }: { children: React.ReactNode }) {
+  const { examSubmitted, resultsDone } = useNavStore();
+  const router = useRouter();
+  const pathname = usePathname();
+
+  useEffect(() => {
+    // Prevent access to /exam after submission
+    if (pathname === "/exam/exam-screen" && examSubmitted) {
+      router.replace("/results");
+    }
+
+    // Prevent access to /results after done
+    if (pathname === "/exam/results" && resultsDone) {
+      router.replace("/categories"); // or wherever you want them to go
+    }
+  }, [pathname, examSubmitted, resultsDone, router]);
+
+  return <>{children}</>;
+}

components/Header.tsx

@@ -32,7 +32,7 @@ const Header = ({
     if (confirmed) {
       stopTimer();
       cancelExam();
-      router.push("/categories");
+      router.replace("/categories");
     }
   };