feat(nav): add flow-guarding for exam result screens

app/exam/results/page.tsx

@@ -1,7 +1,7 @@
 "use client";
 
 import { useRouter } from "next/navigation";
-import React from "react";
+import React, { useEffect } from "react";
 import { ArrowLeft } from "lucide-react";
 import { useExamStore } from "@/stores/examStore";
 import QuestionItem from "@/components/QuestionItem";
@@ -10,7 +10,20 @@ import { getResultViews } from "@/lib/gallery-views";
 
 export default function ResultsPage() {
   const router = useRouter();
-  const { result, clearResult } = useExamStore();
+  const { result, clearResult, setStatus, status } = useExamStore();
+
+  useEffect(() => {
+    const handlePopState = () => {
+      if (status !== "finished") {
+        router.replace(`/categories`);
+      }
+    };
+
+    window.addEventListener("popstate", handlePopState);
+    return () => {
+      window.removeEventListener("popstate", handlePopState);
+    };
+  }, [status, router, setStatus]);
 
   if (!result) {
     return (
@@ -21,8 +34,9 @@ export default function ResultsPage() {
   }
 
   const handleBackToHome = () => {
-    clearResult();
-    router.push("/categories");
+    setStatus("not-started"); // ✅ reset exam flow
+    clearResult(); // ✅ clear stored results
+    router.replace("/categories"); // ✅ prevent re-entry
   };
 
   const views = getResultViews(result);