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/task/auto_purchase.go

@@ -519,6 +519,7 @@ func (h *AutoPurchaseHandler) activateMainPackage(
 		DataResetCycle:            pkg.DataResetCycle,
 		PendingRealnameActivation: pendingRealnameActivation,
 		Generation:                order.Generation,
+		PaidAmount:                order.ActualPaidAmount,
 	}
 
 	if carrierType == constants.AssetWalletResourceTypeIotCard {
@@ -592,6 +593,7 @@ func (h *AutoPurchaseHandler) activateAddonPackage(
 		ExpiresAt:      expiresAt,
 		DataResetCycle: pkg.DataResetCycle,
 		Generation:     order.Generation,
+		PaidAmount:     order.ActualPaidAmount,
 	}
 
 	if carrierType == constants.AssetWalletResourceTypeIotCard {