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

src/Application/TakeoutSaaS.Application/App/Tenants/Validators/CreateAnnouncementCommandValidator.cs

@@ -0,0 +1,35 @@
+using FluentValidation;
+using TakeoutSaaS.Application.App.Tenants.Commands;
+using TakeoutSaaS.Domain.Tenants.Enums;
+
+namespace TakeoutSaaS.Application.App.Tenants.Validators;
+
+/// <summary>
+/// 创建公告命令验证器。
+/// </summary>
+public sealed class CreateAnnouncementCommandValidator : AbstractValidator<CreateTenantAnnouncementCommand>
+{
+    /// <summary>
+    /// 初始化验证规则。
+    /// </summary>
+    public CreateAnnouncementCommandValidator()
+    {
+        RuleFor(x => x.Title)
+            .NotEmpty()
+            .MaximumLength(128);
+
+        RuleFor(x => x.Content)
+            .NotEmpty();
+
+        RuleFor(x => x.TargetType)
+            .NotEmpty();
+
+        RuleFor(x => x)
+            .Must(x => x.TenantId != 0 || x.PublisherScope == PublisherScope.Platform)
+            .WithMessage("TenantId=0 仅允许平台公告");
+
+        RuleFor(x => x.EffectiveTo)
+            .Must((command, effectiveTo) => !effectiveTo.HasValue || command.EffectiveFrom < effectiveTo.Value)
+            .WithMessage("生效开始时间必须早于结束时间");
+    }
+}

src/Application/TakeoutSaaS.Application/App/Tenants/Validators/PublishAnnouncementCommandValidator.cs

@@ -0,0 +1,24 @@
+using FluentValidation;
+using TakeoutSaaS.Application.App.Tenants.Commands;
+
+namespace TakeoutSaaS.Application.App.Tenants.Validators;
+
+/// <summary>
+/// 发布公告命令验证器。
+/// </summary>
+public sealed class PublishAnnouncementCommandValidator : AbstractValidator<PublishAnnouncementCommand>
+{
+    /// <summary>
+    /// 初始化验证规则。
+    /// </summary>
+    public PublishAnnouncementCommandValidator()
+    {
+        RuleFor(x => x.AnnouncementId)
+            .GreaterThan(0);
+
+        RuleFor(x => x.RowVersion)
+            .NotNull()
+            .Must(rowVersion => rowVersion != null && rowVersion.Length > 0)
+            .WithMessage("RowVersion 不能为空");
+    }
+}

src/Application/TakeoutSaaS.Application/App/Tenants/Validators/RevokeAnnouncementCommandValidator.cs

@@ -0,0 +1,24 @@
+using FluentValidation;
+using TakeoutSaaS.Application.App.Tenants.Commands;
+
+namespace TakeoutSaaS.Application.App.Tenants.Validators;
+
+/// <summary>
+/// 撤销公告命令验证器。
+/// </summary>
+public sealed class RevokeAnnouncementCommandValidator : AbstractValidator<RevokeAnnouncementCommand>
+{
+    /// <summary>
+    /// 初始化验证规则。
+    /// </summary>
+    public RevokeAnnouncementCommandValidator()
+    {
+        RuleFor(x => x.AnnouncementId)
+            .GreaterThan(0);
+
+        RuleFor(x => x.RowVersion)
+            .NotNull()
+            .Must(rowVersion => rowVersion != null && rowVersion.Length > 0)
+            .WithMessage("RowVersion 不能为空");
+    }
+}

src/Application/TakeoutSaaS.Application/App/Tenants/Validators/UpdateAnnouncementCommandValidator.cs

@@ -0,0 +1,28 @@
+using FluentValidation;
+using TakeoutSaaS.Application.App.Tenants.Commands;
+
+namespace TakeoutSaaS.Application.App.Tenants.Validators;
+
+/// <summary>
+/// 更新公告命令验证器。
+/// </summary>
+public sealed class UpdateAnnouncementCommandValidator : AbstractValidator<UpdateTenantAnnouncementCommand>
+{
+    /// <summary>
+    /// 初始化验证规则。
+    /// </summary>
+    public UpdateAnnouncementCommandValidator()
+    {
+        RuleFor(x => x.Title)
+            .NotEmpty()
+            .MaximumLength(128);
+
+        RuleFor(x => x.Content)
+            .NotEmpty();
+
+        RuleFor(x => x.RowVersion)
+            .NotNull()
+            .Must(rowVersion => rowVersion != null && rowVersion.Length > 0)
+            .WithMessage("RowVersion 不能为空");
+    }
+}