feat: 新增配额包/支付相关实体与迁移

App：新增 operation_logs/quota_packages/tenant_payments/tenant_quota_package_purchases 表

Identity：修正 Avatar 字段类型（varchar(256)->text），保持现有数据不变

src/Application/TakeoutSaaS.Application/App/Subscriptions/Queries/GetSubscriptionDetailQuery.cs

@@ -0,0 +1,15 @@
+using MediatR;
+using TakeoutSaaS.Application.App.Subscriptions.Dto;
+
+namespace TakeoutSaaS.Application.App.Subscriptions.Queries;
+
+/// <summary>
+/// 查询订阅详情（含套餐信息、配额使用、变更历史）。
+/// </summary>
+public sealed record GetSubscriptionDetailQuery : IRequest<SubscriptionDetailDto?>
+{
+    /// <summary>
+    /// 订阅 ID。
+    /// </summary>
+    public long SubscriptionId { get; init; }
+}