feat: 实现租户列表查询接口

- 获取租户列表：GET /api/admin/v1/tenants
- 用于填充租户下拉选择器

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

src/Api/TakeoutSaaS.AdminApi/Controllers/TenantsController.cs

@@ -0,0 +1,42 @@
+using MediatR;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+using TakeoutSaaS.Application.App.Tenants.Contracts;
+using TakeoutSaaS.Application.App.Tenants.Queries;
+using TakeoutSaaS.Module.Authorization.Attributes;
+using TakeoutSaaS.Shared.Abstractions.Results;
+using TakeoutSaaS.Shared.Web.Api;
+
+namespace TakeoutSaaS.AdminApi.Controllers;
+
+/// <summary>
+/// 租户管理。
+/// </summary>
+[ApiVersion("1.0")]
+[Authorize]
+[Route("api/admin/v{version:apiVersion}/tenants")]
+public sealed class TenantsController(IMediator mediator) : BaseApiController
+{
+    /// <summary>
+    /// 获取租户列表（用于下拉选择器）。
+    /// </summary>
+    /// <param name="keyword">关键字（租户名称/编码）。</param>
+    /// <param name="cancellationToken">取消标记。</param>
+    /// <returns>租户列表。</returns>
+    [HttpGet]
+    [PermissionAuthorize("tenant:read")]
+    [ProducesResponseType(typeof(ApiResponse<IReadOnlyList<TenantListItemDto>>), StatusCodes.Status200OK)]
+    public async Task<ApiResponse<IReadOnlyList<TenantListItemDto>>> List(
+        [FromQuery] string? keyword,
+        CancellationToken cancellationToken)
+    {
+        // 1. 构造查询
+        var query = new ListTenantsQuery { Keyword = keyword };
+
+        // 2. 执行查询
+        var result = await mediator.Send(query, cancellationToken);
+
+        // 3. 返回租户列表
+        return ApiResponse<IReadOnlyList<TenantListItemDto>>.Ok(result);
+    }
+}

src/Application/TakeoutSaaS.Application/App/Tenants/Contracts/TenantListItemDto.cs

@@ -0,0 +1,37 @@
+using System.Text.Json.Serialization;
+using TakeoutSaaS.Domain.Tenants.Enums;
+using TakeoutSaaS.Shared.Abstractions.Serialization;
+
+namespace TakeoutSaaS.Application.App.Tenants.Contracts;
+
+/// <summary>
+/// 租户列表项 DTO（用于下拉选择器）。
+/// </summary>
+public sealed class TenantListItemDto
+{
+    /// <summary>
+    /// 租户 ID（雪花，序列化为字符串）。
+    /// </summary>
+    [JsonConverter(typeof(SnowflakeIdJsonConverter))]
+    public long Id { get; init; }
+
+    /// <summary>
+    /// 租户编码。
+    /// </summary>
+    public string Code { get; init; } = string.Empty;
+
+    /// <summary>
+    /// 租户名称。
+    /// </summary>
+    public string Name { get; init; } = string.Empty;
+
+    /// <summary>
+    /// 租户简称。
+    /// </summary>
+    public string? ShortName { get; init; }
+
+    /// <summary>
+    /// 租户状态。
+    /// </summary>
+    public TenantStatus Status { get; init; }
+}

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

@@ -0,0 +1,30 @@
+using MediatR;
+using TakeoutSaaS.Application.App.Tenants.Contracts;
+using TakeoutSaaS.Application.App.Tenants.Queries;
+using TakeoutSaaS.Domain.Tenants.Repositories;
+
+namespace TakeoutSaaS.Application.App.Tenants.Handlers;
+
+/// <summary>
+/// 获取租户列表查询处理器。
+/// </summary>
+public sealed class ListTenantsQueryHandler(ITenantRepository tenantRepository)
+    : IRequestHandler<ListTenantsQuery, IReadOnlyList<TenantListItemDto>>
+{
+    /// <inheritdoc />
+    public async Task<IReadOnlyList<TenantListItemDto>> Handle(ListTenantsQuery request, CancellationToken cancellationToken)
+    {
+        // 1. 查询租户列表
+        var tenants = await tenantRepository.GetAllAsync(request.Keyword, cancellationToken);
+
+        // 2. 映射 DTO
+        return tenants.Select(t => new TenantListItemDto
+        {
+            Id = t.Id,
+            Code = t.Code,
+            Name = t.Name,
+            ShortName = t.ShortName,
+            Status = t.Status
+        }).ToArray();
+    }
+}

src/Application/TakeoutSaaS.Application/App/Tenants/Queries/ListTenantsQuery.cs

@@ -0,0 +1,15 @@
+using MediatR;
+using TakeoutSaaS.Application.App.Tenants.Contracts;
+
+namespace TakeoutSaaS.Application.App.Tenants.Queries;
+
+/// <summary>
+/// 获取租户列表查询（用于下拉选择器）。
+/// </summary>
+public sealed record ListTenantsQuery : IRequest<IReadOnlyList<TenantListItemDto>>
+{
+    /// <summary>
+    /// 关键字（租户名称/编码）。
+    /// </summary>
+    public string? Keyword { get; init; }
+}

src/Domain/TakeoutSaaS.Domain/Tenants/Repositories/ITenantRepository.cs

@@ -22,4 +22,12 @@ public interface ITenantRepository
     /// <param name="cancellationToken">取消标记。</param>
     /// <returns>租户列表（仅返回找到的租户）。</returns>
     Task<IReadOnlyList<Tenant>> FindByIdsAsync(IReadOnlyCollection<long> tenantIds, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// 获取所有租户列表（用于下拉选择器）。
+    /// </summary>
+    /// <param name="keyword">关键字（租户名称/编码）。</param>
+    /// <param name="cancellationToken">取消标记。</param>
+    /// <returns>租户列表。</returns>
+    Task<IReadOnlyList<Tenant>> GetAllAsync(string? keyword, CancellationToken cancellationToken = default);
 }

src/Infrastructure/TakeoutSaaS.Infrastructure/App/Repositories/EfTenantRepository.cs

@@ -34,4 +34,23 @@ public sealed class EfTenantRepository(TakeoutAdminDbContext context) : ITenantR
             .Where(x => tenantIds.Contains(x.Id))
             .ToListAsync(cancellationToken);
     }
+
+    /// <inheritdoc />
+    public async Task<IReadOnlyList<Tenant>> GetAllAsync(string? keyword, CancellationToken cancellationToken = default)
+    {
+        // 1. 构建基础查询
+        var query = context.Tenants
+            .AsNoTracking()
+            .Where(x => x.DeletedAt == null);
+
+        // 2. 应用关键字过滤
+        if (!string.IsNullOrWhiteSpace(keyword))
+        {
+            var normalized = keyword.Trim();
+            query = query.Where(x => x.Name.Contains(normalized) || x.Code.Contains(normalized));
+        }
+
+        // 3. 返回列表
+        return await query.OrderBy(x => x.Code).ToListAsync(cancellationToken);
+    }
 }