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/TestUtilities/AnnouncementTestData.cs

@@ -0,0 +1,74 @@
+using TakeoutSaaS.Application.App.Tenants.Commands;
+using TakeoutSaaS.Domain.Tenants.Entities;
+using TakeoutSaaS.Domain.Tenants.Enums;
+
+namespace TakeoutSaaS.Application.Tests.TestUtilities;
+
+public static class AnnouncementTestData
+{
+    public static CreateTenantAnnouncementCommand CreateValidCreateCommand()
+        => new()
+        {
+            TenantId = 100,
+            Title = "公告标题",
+            Content = "公告内容",
+            AnnouncementType = TenantAnnouncementType.System,
+            Priority = 1,
+            EffectiveFrom = DateTime.UtcNow.AddHours(-1),
+            EffectiveTo = DateTime.UtcNow.AddHours(2),
+            PublisherScope = PublisherScope.Tenant,
+            TargetType = "ALL_TENANTS",
+            TargetParameters = null
+        };
+
+    public static UpdateTenantAnnouncementCommand CreateValidUpdateCommand()
+        => new()
+        {
+            TenantId = 100,
+            AnnouncementId = 9001,
+            Title = "更新公告",
+            Content = "更新内容",
+            TargetType = "ALL_TENANTS",
+            TargetParameters = null,
+            RowVersion = new byte[] { 1, 2, 3 }
+        };
+
+    public static PublishAnnouncementCommand CreateValidPublishCommand()
+        => new()
+        {
+            AnnouncementId = 9001,
+            RowVersion = new byte[] { 1, 2, 3 }
+        };
+
+    public static RevokeAnnouncementCommand CreateValidRevokeCommand()
+        => new()
+        {
+            AnnouncementId = 9001,
+            RowVersion = new byte[] { 1, 2, 3 }
+        };
+
+    public static TenantAnnouncement CreateAnnouncement(
+        long id,
+        long tenantId,
+        int priority,
+        DateTime effectiveFrom,
+        AnnouncementStatus status = AnnouncementStatus.Draft,
+        bool isActive = false)
+        => new()
+        {
+            Id = id,
+            TenantId = tenantId,
+            Title = $"公告-{id}",
+            Content = "内容",
+            AnnouncementType = TenantAnnouncementType.System,
+            Priority = priority,
+            EffectiveFrom = effectiveFrom,
+            EffectiveTo = null,
+            PublisherScope = PublisherScope.Tenant,
+            Status = status,
+            TargetType = string.Empty,
+            TargetParameters = null,
+            IsActive = isActive,
+            RowVersion = new byte[] { 1, 1, 1 }
+        };
+}