feat: 自动结算返回到期时间戳供前端秒级倒计时

详情/列表用 auto_expire_at_ts 做 HH:MM:SS 时钟；展示不依赖 Celery，真正自动结单才需要 beat。

Co-authored-by: Cursor <cursoragent@cursor.com>

jituan/services/order_deal.py

@@ -55,9 +55,15 @@ def order_auto_settle_payload(order) -> dict:
     elif timezone.is_naive(expire_at) and timezone.is_aware(now):
         expire_at = timezone.make_aware(expire_at, timezone.get_current_timezone())
     remain = int((expire_at - now).total_seconds())
+    try:
+        expire_ts = int(expire_at.timestamp())
+    except Exception:
+        expire_ts = 0
     return {
         'auto_settle_eligible': True,
         'auto_expire_at': fmt_datetime(expire_at),
+        # 前端用时间戳做秒级时钟倒计时，避免解析本地时区偏差
+        'auto_expire_at_ts': expire_ts,
         'auto_settle_remain_seconds': max(0, remain),
     }