优化号主交接超时卡死问题

- 号主交接超时(owner_timeout)后允许补提交交接说明，避免临时延误导致订单卡死
- 后台新增"重置交接"动作，可将超时订单恢复为待号主交接并刷新计时
- 交接超时改以进入待交接时刻为基准计算，新增 handoff_started_at 字段

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

backend/internal/modules/order/lifecycle.go

@@ -177,8 +177,10 @@ func (r *Repository) ConfirmPaidFromChannelTx(tx *gorm.DB, orderID uint64) (uint
 
 	// 租客已通过外部渠道付款，这里不写租客钱包流水。
 	orderID = order.ID
+	now := time.Now()
 	order.Status = orderStatusPendingHandoff
 	order.HandoffStatus = handoffStatusPendingOwner
+	order.HandoffStartedAt = &now
 	markAssetsRented(listing, account)
 	conv, err := chat.EnsureOrderConversation(tx, *order)
 	if err != nil {