feat(admin): 新增管理员角色、账单、订阅、套餐管理功能

- 新增 AdminRolesController 实现角色 CRUD 和权限管理
- 新增 BillingsController 实现账单查询功能
- 新增 SubscriptionsController 实现订阅管理功能
- 新增 TenantPackagesController 实现套餐管理功能
- 新增租户详情、配额使用、账单列表等查询功能
- 新增 TenantPackage、TenantSubscription 等领域实体
- 新增相关枚举：SubscriptionStatus、TenantPackageType 等
- 更新 appsettings 配置文件
- 更新权限授权策略提供者

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/Application/TakeoutSaaS.Application/App/Tenants/Handlers/GetTenantBillingsQueryHandler.cs

@@ -0,0 +1,56 @@
+using MediatR;
+using TakeoutSaaS.Application.App.Tenants.Contracts;
+using TakeoutSaaS.Application.App.Tenants.Queries;
+using TakeoutSaaS.Domain.Tenants.Repositories;
+using TakeoutSaaS.Shared.Abstractions.Results;
+
+namespace TakeoutSaaS.Application.App.Tenants.Handlers;
+
+/// <summary>
+/// 获取租户账单列表查询处理器。
+/// </summary>
+public sealed class GetTenantBillingsQueryHandler(ITenantRepository tenantRepository)
+    : IRequestHandler<GetTenantBillingsQuery, PagedResult<TenantBillingListDto>>
+{
+    /// <inheritdoc />
+    public async Task<PagedResult<TenantBillingListDto>> Handle(
+        GetTenantBillingsQuery request,
+        CancellationToken cancellationToken)
+    {
+        // 1. 查询租户账单（分页）
+        var (billings, totalCount) = await tenantRepository.GetBillingsAsync(
+            request.TenantId,
+            request.Page,
+            request.PageSize,
+            cancellationToken);
+
+        // 2. 获取租户名称
+        var tenant = await tenantRepository.FindByIdAsync(request.TenantId, cancellationToken);
+        var tenantName = tenant?.Name;
+
+        // 3. 映射为 DTO
+        var items = billings.Select(b => new TenantBillingListDto
+        {
+            Id = b.Id,
+            TenantId = b.TenantId,
+            TenantName = tenantName,
+            StatementNo = b.StatementNo,
+            BillingType = b.BillingType,
+            PeriodStart = b.PeriodStart,
+            PeriodEnd = b.PeriodEnd,
+            AmountDue = b.AmountDue,
+            AmountPaid = b.AmountPaid,
+            DiscountAmount = b.DiscountAmount,
+            TaxAmount = b.TaxAmount,
+            Currency = b.Currency,
+            Status = b.Status,
+            DueDate = b.DueDate,
+            OverdueNotifiedAt = b.OverdueNotifiedAt,
+            CreatedAt = b.CreatedAt,
+            UpdatedAt = b.UpdatedAt
+        }).ToList();
+
+        // 4. 返回分页结果
+        return new PagedResult<TenantBillingListDto>(items, totalCount, request.Page, request.PageSize);
+    }
+}