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

migrations/000129_add_paid_amount_to_package_usage.down.sql

@@ -0,0 +1 @@
+ALTER TABLE tb_package_usage DROP COLUMN IF EXISTS paid_amount;

migrations/000129_add_paid_amount_to_package_usage.up.sql

@@ -0,0 +1,15 @@
+-- 为 tb_package_usage 新增购买实付金额快照字段
+-- paid_amount: 购买时从订单复制的实付金额（分），nullable
+-- 线下支付或企业无订单分配时为 null
+ALTER TABLE tb_package_usage ADD COLUMN IF NOT EXISTS paid_amount BIGINT;
+
+COMMENT ON COLUMN tb_package_usage.paid_amount IS '购买实付金额快照（分，从订单复制，无订单或线下支付时为null）';
+
+-- 存量数据回填：通过 order_id 关联 tb_order 回填 actual_paid_amount
+-- order_id = 0 的记录（企业无订单分配）保持 null，语义正确
+UPDATE tb_package_usage pu
+SET paid_amount = o.actual_paid_amount
+FROM tb_order o
+WHERE pu.order_id = o.id
+  AND pu.order_id != 0
+  AND pu.paid_amount IS NULL;