feat: 新增套餐使用记录实付金额快照字段 paid_amount

- 新增迁移 000129：tb_package_usage 添加 paid_amount BIGINT 字段，存量数据通过 JOIN tb_order 回填
- PackageUsage Model 新增 PaidAmount *int64 字段
- 4 个写入点（order service 主套餐/加油包、auto_purchase 主套餐/加油包）赋值 order.ActualPaidAmount
- AssetPackageResponse DTO 新增 paid_amount 字段
- GetCurrentPackage / GetPackages 填充 paid_amount，接口直接返回购买价格无需 JOIN 订单表

internal/service/asset/service.go

@@ -693,6 +693,7 @@ func (s *Service) GetPackages(ctx context.Context, assetType string, id uint, pa
 			ExpiresAt:         u.ExpiresAt,
 			MasterUsageID:     u.MasterUsageID,
 			Priority:          u.Priority,
+			PaidAmount:        u.PaidAmount,
 			CreatedAt:         u.CreatedAt,
 		}
 		all = append(all, item)
@@ -770,6 +771,7 @@ func (s *Service) GetCurrentPackage(ctx context.Context, assetType string, id ui
 		ExpiresAt:         usage.ExpiresAt,
 		MasterUsageID:     usage.MasterUsageID,
 		Priority:          usage.Priority,
+		PaidAmount:        usage.PaidAmount,
 		CreatedAt:         usage.CreatedAt,
 	}, nil
 }

internal/service/order/service.go

@@ -1843,6 +1843,7 @@ func (s *Service) activateMainPackage(ctx context.Context, tx *gorm.DB, order *m
 		Priority:                  priority,
 		DataResetCycle:            pkg.DataResetCycle,
 		PendingRealnameActivation: pendingRealnameActivation,
+		PaidAmount:                order.ActualPaidAmount,
 	}
 
 	if carrierType == "iot_card" {
@@ -1928,6 +1929,7 @@ func (s *Service) activateAddonPackage(ctx context.Context, tx *gorm.DB, order *
 		ActivatedAt:    &activatedAt,
 		ExpiresAt:      &expiresAt,
 		DataResetCycle: pkg.DataResetCycle,
+		PaidAmount:     order.ActualPaidAmount,
 	}
 
 	if carrierType == "iot_card" {