回调优化为单地址 upsert 配置并支持重置密钥

- 回调订阅改为单记录 upsert：保存即覆盖（URL/事件/状态），自动停用其他订阅，无新增/删除
- 新增重置密钥：保存时传 rotate_secret=true 重新生成密钥并返回一次，解决密钥丢失无法找回
- 删除不再使用的 PATCH /callbacks/:id/status 路由及对应 handler/service 死代码
- 前端回调页改为内联表单（URL/事件/状态），新增重置密钥按钮（确认后展示新密钥一次）
- 补充单地址复用、disabled 不投递、密钥轮换测试

backend/internal/service/fulfillment.go

@@ -240,9 +240,9 @@ func (s *FulfillmentService) CreateTestOrder(in CreateTestOrderInput) (*model.Fu
 		in.OrderStatus = model.OrderStatusPaid
 	}
 	switch in.OrderStatus {
-	case model.OrderStatusPaid, model.OrderStatusShipFailed:
+	case model.OrderStatusPaid, model.OrderStatusShipFailed, model.OrderStatusCancelled:
 	default:
-		return nil, errors.New("测试订单仅支持已支付待发货或发货失败状态")
+		return nil, errors.New("测试订单仅支持已支付待发货、发货失败或已取消状态")
 	}
 
 	requestData := map[string]interface{}{
@@ -301,13 +301,18 @@ func (s *FulfillmentService) CreateTestOrder(in CreateTestOrderInput) (*model.Fu
 		if in.OrderStatus == model.OrderStatusShipFailed {
 			order.FailureReason = fallbackName(in.Note, "联调测试订单初始化为发货失败，可重新发货")
 		}
+		if in.OrderStatus == model.OrderStatusCancelled {
+			now := time.Now()
+			order.CancelledAt = &now
+		}
 		if err := tx.Create(order).Error; err != nil {
 			return err
 		}
+		canShip, _ := CanFulfill(order)
 		if err := writeAudit(tx, &in.MerchantID, &in.ActorUserID, nil, "merchant_test_order.create", "fulfillment_order", order.OrderNo, map[string]interface{}{
 			"sku":          in.SKU,
 			"order_status": in.OrderStatus,
-			"can_ship":     true,
+			"can_ship":     canShip,
 		}); err != nil {
 			return err
 		}
@@ -798,15 +803,15 @@ type DashboardStats struct {
 	UserCount                 int64  `json:"user_count"`
 	OrderCount                int64  `json:"order_count"`
 	TodayOrderCount           int64  `json:"today_order_count"`
-	TotalSales                int64                 `json:"total_sales"`
-	TodaySales                int64                 `json:"today_sales"`
-	TotalFees                 int64                 `json:"total_fees"`
-	TodayFees                 int64                 `json:"today_fees"`
-	PaidOrderCount            int64                 `json:"paid_order_count"`
-	DeliveringOrderCount      int64                 `json:"delivering_order_count"`
-	DeliveredOrderCount       int64                 `json:"delivered_order_count"`
-	ShipFailedOrderCount      int64                 `json:"ship_failed_order_count"`
-	CancelledOrderCount       int64                 `json:"cancelled_order_count"`
+	TotalSales                int64  `json:"total_sales"`
+	TodaySales                int64  `json:"today_sales"`
+	TotalFees                 int64  `json:"total_fees"`
+	TodayFees                 int64  `json:"today_fees"`
+	PaidOrderCount            int64  `json:"paid_order_count"`
+	DeliveringOrderCount      int64  `json:"delivering_order_count"`
+	DeliveredOrderCount       int64  `json:"delivered_order_count"`
+	ShipFailedOrderCount      int64  `json:"ship_failed_order_count"`
+	CancelledOrderCount       int64  `json:"cancelled_order_count"`
 	WalletAvailableBalance    int64  `json:"wallet_available_balance"`
 	WalletFrozenBalance       int64  `json:"wallet_frozen_balance"`
 	APIClientCount            int64  `json:"api_client_count"`