4. Add `GET /api/v1/admin/courses/:id/modules/:moduleId/quizzes/:quizId/analytics` endpoint

[DeFiVC]

What: Add an admin endpoint that returns detailed analytics for a specific quiz (question-by-question performance, average time, common wrong answers).

Why: Quiz analytics help course creators identify problematic questions and improve content quality.

Scope: Create endpoint that analyzes: question-by-question correct rate, average time per question, common wrong answers, score distribution, attempt patterns.

Acceptance criteria:

• Returns question-by-question analytics
• Includes correct rates and common wrong answers
• Shows score distribution
• Cached for 5 minutes

Technical context: src/modules/quizzes/quiz.service.ts — quiz queries. src/database/schema.ts:113-142 — quizSubmissions.

---