功能：平台管理员删除商户账号

backend/internal/service/user.go

@@ -316,3 +316,31 @@ func (s *UserService) DeletePlatformAdmin(id, actorUserID uint) error {
 		return tx.Delete(&user).Error
 	})
 }
+
+// DeleteMerchantAccount permanently removes a merchant login account and all
+// of its merchant memberships. Platform administrators must be managed from
+// the dedicated platform administrator view instead.
+func (s *UserService) DeleteMerchantAccount(id, actorUserID uint) error {
+	if id == 0 {
+		return errors.New("用户不存在")
+	}
+	if id == actorUserID {
+		return errors.New("不能删除当前登录账号")
+	}
+	return s.db.Transaction(func(tx *gorm.DB) error {
+		var user model.User
+		if err := tx.First(&user, id).Error; err != nil {
+			if errors.Is(err, gorm.ErrRecordNotFound) {
+				return errors.New("用户不存在")
+			}
+			return err
+		}
+		if user.Role != model.RoleMerchant {
+			return errors.New("平台管理员请在平台管理员列表中管理")
+		}
+		if err := tx.Where("user_id = ?", user.ID).Delete(&model.MerchantMember{}).Error; err != nil {
+			return err
+		}
+		return tx.Delete(&user).Error
+	})
+}