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/constants.go

@@ -21,6 +21,7 @@ const (
 	handoffStatusPendingOwnerCheckout  = "pending_owner_checkout"
 	handoffStatusPendingRenterCheckout = "pending_renter_checkout"
 	handoffStatusReturned              = "returned"
+	handoffStatusOwnerTimeout          = "owner_timeout"
 	handoffStatusCancelled             = "cancelled"
 	handoffStatusAdminClosed           = "admin_closed"
 	handoffStatusAdminAbnormal         = "admin_abnormal"