test(business): 业务数据管理模块集成用例（70 例）与两处缺陷修复

- 覆盖：编号格式与序号递增/状态机终态拦截/三处汇总冗余一致性/跨业务批次
  400/已核算禁改禁删/毛利润金标准与防除零/asOf 回溯/评级重叠/审计双记录
- 缺陷修复①：change_status 留痕 old_status 取到赋值后属性（时间线失真 3→3）
- 缺陷修复②：freight_amount 漏金额校验（负数/三位小数可落库污染运费合计）
- conftest 扩展业务六表清理（编号前缀 + FK 逆序收口）与评级种子基线恢复
- 全量回归 603 passed（单元 381 / 集成 222）

Co-Authored-By: Claude Code <noreply@anthropic.com>

backend/app/services/business_service.py

@@ -511,12 +511,15 @@ def change_status(
         if business.status == payload.status:
             raise BadRequestError("状态未变化")
 
+        # 变更前状态须在赋值前固化：ORM 属性赋值后 old_status 就取不到旧值
+        # （留痕会记成 old==new 失真，时间线无法回溯）
+        old_status = business.status
         business.status = payload.status
         business_repository.add_status_log(
             session,
             BusinessStatusLog(
                 business_id=business_id,
-                old_status=business.status,
+                old_status=old_status,
                 new_status=payload.status,
                 change_reason=payload.reason,
                 operator_id=operator.id,
@@ -528,7 +531,7 @@ def change_status(
         logger.info(
             "业务状态变更 | business_id=%s | %s -> %s",
             business_id,
-            business.status,
+            old_status,
             payload.status,
         )
         return out