fix(cma): AU-001 day_cum_amount 返回日累计(day_total) 而非拆单累计

day_cum_amount 原返回 cum_same(同收款方拆单累计)，与字段语义(日累计)不符；
日累计升级用例 T8 期望 day_cum=当日同提交人累计。改为 day_total。

Ref: 0-P0-project-20260915-cma-treasury-stage1 自验 T8

backend/app/api/treasury.py

@@ -235,7 +235,7 @@ def _eval_au001(db, entity_id, payment, rule) -> dict:
     basis = (f"单笔 {amount} 档位 {base_scope}→{base_req}级；拆单累计（同提交人×同收款方×同自然日）{cum_same}"
              f"→{cum_req}级；取最严={required}级；边界左闭右开")
     return {"rule_code": "AU-001", "verdict": "pass", "severity": rule.severity,
-            "required_approvals": required, "day_cum_amount": cum_same,
+            "required_approvals": required, "day_cum_amount": day_total,
             "detail": _hit_detail("AU-001", rule.rule_version, matched_scope,
                                   _r(daily_cum_limit) if daily_cum_limit is not None else None,
                                   cum_same, basis)}