feat: finalize core modules and gateway

src/Core/TakeoutSaaS.Shared.Abstractions/Entities/MultiTenantEntityBase.cs

@@ -0,0 +1,12 @@
+namespace TakeoutSaaS.Shared.Abstractions.Entities;
+
+/// <summary>
+/// 多租户审计实体基类：提供租户标识、审计字段与软删除标记。
+/// </summary>
+public abstract class MultiTenantEntityBase : AuditableEntityBase, IMultiTenantEntity
+{
+    /// <summary>
+    /// 所属租户 ID。
+    /// </summary>
+    public Guid TenantId { get; set; }
+}