chore: add optimistic locking to Coupon entity with @Version field

Author: yeonjiyeon

apps/commerce-api/src/main/java/com/loopers/domain/coupon/Coupon.java

@@ -8,6 +8,7 @@
 import jakarta.persistence.EnumType;
 import jakarta.persistence.Enumerated;
 import jakarta.persistence.Table;
+import jakarta.persistence.Version;
 import lombok.AccessLevel;
 import lombok.NoArgsConstructor;
 
@@ -16,6 +17,9 @@
 @NoArgsConstructor(access = AccessLevel.PROTECTED)
 public class Coupon extends BaseEntity {
 
+  @Version
+  private long version;
+
   @Column(name = "ref_user_id", nullable = false)
   private long userId;