feat(03-01): add GwSessionAffinityConfig value object

- Created session affinity configuration value object
- Includes Enabled, Policy, AffinityKeyName fields
- Supports Header and Cookie policies

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

@@ -0,0 +1,22 @@
+namespace Fengling.Platform.Domain.AggregatesModel.GatewayAggregate;
+
+/// <summary>
+/// 会话亲和配置（值对象）
+/// </summary>
+public class GwSessionAffinityConfig
+{
+    /// <summary>
+    /// 是否启用会话亲和
+    /// </summary>
+    public bool Enabled { get; set; }
+    
+    /// <summary>
+    /// 策略：Header, Cookie
+    /// </summary>
+    public string Policy { get; set; } = "Header";
+    
+    /// <summary>
+    /// 亲和键名称
+    /// </summary>
+    public string AffinityKeyName { get; set; } = "X-Session-Key";
+}