feat(coupon): 设置优惠券最低消费金额默认值为0

- 引入BigDecimal类以支持金额计算
- 在插入数据库前检查并设置最低消费金额默认值
- 确保所有新创建的优惠券都有有效的最低消费门槛

alien-store-platform/src/main/java/shop/alien/storeplatform/service/impl/LifeDiscountCouponPlatformServiceImpl.java

@@ -19,6 +19,7 @@ import shop.alien.storeplatform.service.LifeDiscountCouponPlatformService;
 import shop.alien.storeplatform.service.LifeDiscountCouponQuantumRulesPlatformService;
 import shop.alien.util.common.constant.DiscountCouponEnum;
 
+import java.math.BigDecimal;
 import java.time.Instant;
 import java.time.LocalDate;
 import java.time.LocalDateTime;
@@ -96,6 +97,11 @@ public class LifeDiscountCouponPlatformServiceImpl extends ServiceImpl<LifeDisco
                     lifeDiscountCoupon.setValidDate(validDateLocalDate);
                 }
             }
+
+            if (lifeDiscountCoupon.getMinimumSpendingAmount() == null) {
+                lifeDiscountCoupon.setMinimumSpendingAmount(BigDecimal.valueOf(0));
+            }
+
             lifeDiscountCouponMapper.insert(lifeDiscountCoupon);
             //发布优惠券规则信息
             //周中规则保存