feat(03-01): add GwDestination value object

- Created destination endpoint value object embedded in GwCluster
- Includes DestinationId, Address, Health, Weight, HealthStatus, Status fields
- Compatible with YARP Destination config structure

Fengling.Platform.Domain/AggregatesModel/GatewayAggregate/GwDestination.cs

@@ -0,0 +1,37 @@
+namespace Fengling.Platform.Domain.AggregatesModel.GatewayAggregate;
+
+/// <summary>
+/// 目标端点（值对象，内嵌于 GwCluster）
+/// </summary>
+public class GwDestination
+{
+    /// <summary>
+    /// 目标标识
+    /// </summary>
+    public string DestinationId { get; set; } = string.Empty;
+    
+    /// <summary>
+    /// 后端地址
+    /// </summary>
+    public string Address { get; set; } = string.Empty;
+    
+    /// <summary>
+    /// 健康检查端点
+    /// </summary>
+    public string? Health { get; set; }
+    
+    /// <summary>
+    /// 权重（用于加权负载均衡）
+    /// </summary>
+    public int Weight { get; set; } = 1;
+    
+    /// <summary>
+    /// 健康状态
+    /// </summary>
+    public int HealthStatus { get; set; } = 1;
+    
+    /// <summary>
+    /// 状态
+    /// </summary>
+    public int Status { get; set; } = 1;
+}