feat(03-01): add GwCluster aggregate root

- Created cluster aggregate root with string Id (GUID)
- Includes ClusterId, Name, Description, Destinations list
- Embeds GwHealthCheckConfig and GwSessionAffinityConfig
- Includes audit fields: CreatedBy, CreatedTime, UpdatedBy, UpdatedTime
- Supports IsDeleted soft delete and Version for optimistic concurrency

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

@@ -0,0 +1,79 @@
+namespace Fengling.Platform.Domain.AggregatesModel.GatewayAggregate;
+
+/// <summary>
+/// 网关集群聚合根 - 表示后端服务集群配置
+/// </summary>
+public class GwCluster
+{
+    public string Id { get; set; } = Guid.CreateVersion7().ToString("N");
+    
+    /// <summary>
+    /// 集群业务标识
+    /// </summary>
+    public string ClusterId { get; set; } = string.Empty;
+    
+    /// <summary>
+    /// 集群名称
+    /// </summary>
+    public string Name { get; set; } = string.Empty;
+    
+    /// <summary>
+    /// 描述
+    /// </summary>
+    public string? Description { get; set; }
+    
+    /// <summary>
+    /// 目标端点列表（内嵌）
+    /// </summary>
+    public List<GwDestination> Destinations { get; set; } = new();
+    
+    /// <summary>
+    /// 负载均衡策略
+    /// </summary>
+    public string LoadBalancingPolicy { get; set; } = "RoundRobin";
+    
+    /// <summary>
+    /// 健康检查配置
+    /// </summary>
+    public GwHealthCheckConfig? HealthCheck { get; set; }
+    
+    /// <summary>
+    /// 会话亲和配置
+    /// </summary>
+    public GwSessionAffinityConfig? SessionAffinity { get; set; }
+    
+    /// <summary>
+    /// 状态
+    /// </summary>
+    public int Status { get; set; } = 1;
+    
+    /// <summary>
+    /// 创建人ID
+    /// </summary>
+    public long? CreatedBy { get; set; }
+    
+    /// <summary>
+    /// 创建时间
+    /// </summary>
+    public DateTime CreatedTime { get; set; } = DateTime.UtcNow;
+    
+    /// <summary>
+    /// 更新人ID
+    /// </summary>
+    public long? UpdatedBy { get; set; }
+    
+    /// <summary>
+    /// 更新时间
+    /// </summary>
+    public DateTime? UpdatedTime { get; set; }
+    
+    /// <summary>
+    /// 是否删除
+    /// </summary>
+    public bool IsDeleted { get; set; } = false;
+    
+    /// <summary>
+    /// 版本号，用于乐观并发
+    /// </summary>
+    public int Version { get; set; } = 0;
+}