修复订单金额落库不对的问题

migrations/000150_add_cost_price_and_retail_amount.down.sql

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+-- 回滚：删除新增字段
+ALTER TABLE tb_order_item
+    DROP COLUMN IF EXISTS cost_price;
+
+ALTER TABLE tb_package_usage
+    DROP COLUMN IF EXISTS retail_amount;

migrations/000150_add_cost_price_and_retail_amount.up.sql

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+-- 修正订单价格语义：新增成本价字段和零售价快照字段
+-- tb_order_item 新增 cost_price：存储成本单价快照，unit_price 语义修正为零售单价
+ALTER TABLE tb_order_item
+    ADD COLUMN IF NOT EXISTS cost_price BIGINT NOT NULL DEFAULT 0;
+
+COMMENT ON COLUMN tb_order_item.cost_price IS '成本单价快照（分，代购/钱包支付场景为买家成本，平台自营或赠送时为0）';
+
+-- tb_package_usage 新增 retail_amount：存储零售价快照，paid_amount 继续存储成本价
+ALTER TABLE tb_package_usage
+    ADD COLUMN IF NOT EXISTS retail_amount BIGINT;
+
+COMMENT ON COLUMN tb_package_usage.retail_amount IS '购买零售价快照（分，从订单 total_amount 复制，无订单关联时为null）';