feat: 客服封存订单功能（号主失联场景）

新增客服「封存订单」动作，用于号主失联、无法联系的场景：单事务内
完成关闭订单、全量原路退款、永久封存关联商品、解散发布群、双方通知
与审计日志。

- 新增 listing 终态 sealed（封存），区别于可恢复的 offline
- listingLockedForOwnerMutation 锁定 sealed，号主无法再编辑/提审/上架
- 解散群聊按 listing_id 查发布群（listing_group）置 archived，
  阻断所有成员发言并留系统消息
- 新增 order.AdminSeal 及 /admin/orders/:id/seal 路由
- 前端：卖家页 PC/移动端 sealed 视为终态禁用操作，客服后台新增
  「封存订单」按钮与二次确认

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

backend/internal/router/router.go

@@ -188,6 +188,7 @@ func New(cfg config.Config, deps Dependencies, logger *zap.Logger) *gin.Engine {
 	if deps.DB != nil {
 		orderRepo = order.NewRepository(deps.DB, order.Dependencies{
 			ChatNotifier: chatRepo,
+			ChatArchiver: chat.NewOrderChatArchiverAdapter(),
 			RefundStarter: order.RefundStarterFunc(func(ctx context.Context, orderID uint64, refundAmountCent int64, bizType string, remark string) (string, error) {
 				if paymentRepo == nil {
 					return "", order.ErrDependencyUnavailable
@@ -518,6 +519,7 @@ func New(cfg config.Config, deps Dependencies, logger *zap.Logger) *gin.Engine {
 			adminRoutes.GET("/orders/:id", requirePerm("order:view"), orderHandler.AdminDetail)
 			adminRoutes.GET("/orders/:id/handoff-records", requirePerm("order:view"), orderHandler.AdminHandoffRecords)
 			adminRoutes.POST("/orders/:id/close", requirePerm("order:close"), orderHandler.AdminClose)
+			adminRoutes.POST("/orders/:id/seal", requirePerm("order:close"), orderHandler.AdminSeal)
 			adminRoutes.POST("/orders/:id/mark-abnormal", requirePerm("order:mark_abnormal"), orderHandler.AdminMarkAbnormal)
 			adminRoutes.POST("/orders/:id/reset-handoff", requirePerm("order:mark_abnormal"), orderHandler.AdminResetHandoff)
 			adminRoutes.POST("/orders/:id/refund", requirePerm("order:close"), orderHandler.AdminRefund)