feat: Sprint 2 — test taking + results

Backend:
- Models: TestAttempt, AttemptAnswer (migration 002)
- POST /api/attempts: start attempt, shuffle questions/answers,
  hide is_correct, expose is_multiple for UI hints
- POST /api/attempts/{id}/submit: save answers, calculate score,
  strict matching (selected == correct), return full result
- GET /api/attempts/{id}/result: fetch saved result
- Register attempts router in main.py

Frontend:
- api/attempts.ts: types + API functions
- TestTake page: one question at a time, progress bar, timer
  with auto-submit, back navigation controlled by test setting,
  radio/checkbox based on is_multiple
- AttemptResult page: score, pass/fail, per-question breakdown
  with correct/selected/missed answer highlighting
- App.tsx: add /tests/:testId/take and /attempts/:id/result routes
- TestDetail: add "Пройти тест" button

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

backend/alembic/env.py

@@ -15,7 +15,7 @@ if config.config_file_name is not None:
 # Берём DATABASE_URL из настроек приложения
 from app.config import settings
 from app.database import Base
-from app.models import test  # noqa: F401 — импортируем модели, чтобы Alembic их видел
+from app.models import attempt, test  # noqa: F401 — импортируем модели, чтобы Alembic их видел
 
 config.set_main_option("sqlalchemy.url", settings.database_url)