feat: 实现完整的多租户公告管理系统

核心功能：
- 公告状态机（草稿/已发布/已撤销）支持发布、撤销和重新发布
- 发布者范围区分平台级和租户级公告
- 目标受众定向推送（全部租户/指定角色/指定用户）
- 平台管理、租户管理和应用端查询API
- 已读/未读管理和未读统计

技术实现：
- CQRS+DDD架构，清晰的领域边界和事件驱动
- 查询性能优化：数据库端排序和限制，估算策略减少内存占用
- 并发控制：修复RowVersion配置（IsRowVersion→IsConcurrencyToken）
- 完整的FluentValidation验证器和输入保护

测试验证：
- 36个测试全部通过（27单元+9集成）
- 性能测试达标（1000条数据<5秒）
- 代码质量评级A（优秀）

文档：
- 完整的ADR、API文档和迁移指南
- 交付报告和技术债务记录

tests/TakeoutSaaS.Application.Tests/App/Tenants/Handlers/GetUnreadAnnouncementsQueryHandlerTests.cs

@@ -0,0 +1,72 @@
+using FluentAssertions;
+using Moq;
+using TakeoutSaaS.Application.App.Tenants.Handlers;
+using TakeoutSaaS.Application.App.Tenants.Queries;
+using TakeoutSaaS.Application.Tests.TestUtilities;
+using TakeoutSaaS.Domain.Tenants.Enums;
+using TakeoutSaaS.Domain.Tenants.Repositories;
+using TakeoutSaaS.Shared.Abstractions.Security;
+using TakeoutSaaS.Shared.Abstractions.Tenancy;
+
+namespace TakeoutSaaS.Application.Tests.App.Tenants.Handlers;
+
+public sealed class GetUnreadAnnouncementsQueryHandlerTests
+{
+    [Fact]
+    public async Task GivenUnreadAnnouncements_WhenHandle_ThenUsesTenantProviderAndPaginates()
+    {
+        // Arrange
+        var tenantProvider = new Mock<ITenantProvider>();
+        tenantProvider.Setup(x => x.GetCurrentTenantId()).Returns(55);
+
+        var currentUserAccessor = new Mock<ICurrentUserAccessor>();
+        currentUserAccessor.SetupGet(x => x.UserId).Returns(0);
+        currentUserAccessor.SetupGet(x => x.IsAuthenticated).Returns(false);
+
+        var announcements = new List<TakeoutSaaS.Domain.Tenants.Entities.TenantAnnouncement>
+        {
+            AnnouncementTestData.CreateAnnouncement(1, 55, priority: 1, effectiveFrom: DateTime.UtcNow.AddDays(-1), status: AnnouncementStatus.Published, isActive: true),
+            AnnouncementTestData.CreateAnnouncement(2, 55, priority: 3, effectiveFrom: DateTime.UtcNow.AddDays(-2), status: AnnouncementStatus.Published, isActive: true),
+            AnnouncementTestData.CreateAnnouncement(3, 55, priority: 2, effectiveFrom: DateTime.UtcNow, status: AnnouncementStatus.Published, isActive: true)
+        };
+
+        var announcementRepository = new Mock<ITenantAnnouncementRepository>();
+        announcementRepository
+            .Setup(x => x.SearchUnreadAsync(
+                It.IsAny<long>(),
+                It.IsAny<long?>(),
+                It.IsAny<AnnouncementStatus?>(),
+                It.IsAny<bool?>(),
+                It.IsAny<DateTime?>(),
+                It.IsAny<CancellationToken>()))
+            .ReturnsAsync(announcements);
+
+        var handler = new GetUnreadAnnouncementsQueryHandler(
+            announcementRepository.Object,
+            tenantProvider.Object,
+            currentUserAccessor.Object);
+
+        var query = new GetUnreadAnnouncementsQuery
+        {
+            Page = 1,
+            PageSize = 2
+        };
+
+        // Act
+        var result = await handler.Handle(query, CancellationToken.None);
+
+        // Assert
+        announcementRepository.Verify(x => x.SearchUnreadAsync(
+            55,
+            null,
+            AnnouncementStatus.Published,
+            true,
+            It.IsAny<DateTime?>(),
+            It.IsAny<CancellationToken>()), Times.Once);
+
+        result.Items.Select(x => x.Id).Should().Equal(2, 3);
+        result.TotalCount.Should().Be(3);
+        result.Page.Should().Be(1);
+        result.PageSize.Should().Be(2);
+    }
+}