fix : [#5] 동시성 테스트 수정

- `@Lock`, `@Transactional` 사용

src/main/java/hhplus/lecture/application/service/RegistrationService.java

@@ -7,11 +7,13 @@
 import hhplus.lecture.infrastructure.repository.LectureItemRepository;
 import hhplus.lecture.infrastructure.repository.RegistrationRepository;
 import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
 
 import java.time.LocalDateTime;
 import java.util.List;
 
 @Service
+@Transactional
 public class RegistrationService {
 
     private final LectureService lectureService;

src/main/java/hhplus/lecture/infrastructure/repository/LectureItemRepository.java

@@ -1,14 +1,17 @@
 package hhplus.lecture.infrastructure.repository;
 
 import hhplus.lecture.infrastructure.persistence.LectureItemEntity;
+import jakarta.persistence.LockModeType;
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Lock;
 
 import java.time.LocalDate;
 import java.util.List;
 
 public interface LectureItemRepository extends JpaRepository<LectureItemEntity, String> {
 
     // 특강 정보
+    @Lock(LockModeType.PESSIMISTIC_WRITE)
     LectureItemEntity findByLectureItemCode(String lectureItemCode);
 
     List<LectureItemEntity> findAllByLectureDate(LocalDate targetDate);