Add quiz feature: student UI, admin editor, lesson page integration

- QuizSection component: shows questions as text inputs, read-only after submission
- QuizEditor component: admin CRUD for quiz questions with type selector
- saveQuiz/deleteQuiz server actions for admin
- submitQuizAttempt server action: idempotent, auto-marks lesson complete
- Student lesson page: renders QuizSection, updates complete button logic
- Admin lesson page: renders QuizEditor below homework section

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/actions/student-actions.ts

@@ -94,6 +94,43 @@ export async function submitHomework(
   revalidatePath(`/courses/${slug}/lessons/${lessonId}`);
 }
 
+// ── Quiz ──────────────────────────────────────────────────────────────────────
+
+export async function submitQuizAttempt(
+  quizId: string,
+  lessonId: string,
+  slug: string,
+  answers: Record<string, string>
+) {
+  const session = await auth.api.getSession({ headers: await headers() });
+  if (!session) throw new Error("Unauthorized");
+
+  const existing = await prisma.quizAttempt.findFirst({
+    where: { quizId, userId: session.user.id },
+  });
+  if (existing) return;
+
+  await prisma.$transaction(async (tx) => {
+    await tx.quizAttempt.create({
+      data: {
+        userId: session.user.id,
+        quizId,
+        score: 0,
+        answers: answers as object,
+      },
+    });
+    await tx.lessonProgress.upsert({
+      where: { userId_lessonId: { userId: session.user.id, lessonId } },
+      create: { userId: session.user.id, lessonId },
+      update: {},
+    });
+  });
+
+  revalidatePath(`/courses/${slug}/lessons/${lessonId}`);
+  revalidatePath(`/courses/${slug}`);
+  revalidatePath("/dashboard");
+}
+
 // ── Comments ──────────────────────────────────────────────────────────────────
 
 export async function addComment(lessonId: string, slug: string, text: string) {