fix: 修复公告模块核心问题并完善功能

主要修复内容：
1. 修复 RowVersion 并发控制
   - 配置 EF Core RowVersion 映射为 bytea 类型
   - 添加 PostgreSQL 触发器自动生成 RowVersion
   - 在更新/发布/撤销操作中添加 RowVersion 校验
   - 移除 Application 层对 EF Core 的直接依赖

2. 修复 API 路由和校验问题
   - 添加平台公告列表路由的版本化别名
   - 租户公告接口添加 X-Tenant-Id 必填校验，返回 400
   - 生效时间校验返回 422 而非 500
   - 修复 FluentValidation 异常命名冲突

3. 实现关键词搜索功能
   - 在查询参数中添加 keyword 字段
   - 使用 PostgreSQL ILIKE 实现大小写不敏感搜索
   - 支持标题和内容字段的模糊匹配

4. 数据库迁移
   - 新增 RowVersion 触发器迁移文件
   - 回填现有公告记录的 RowVersion

src/Infrastructure/TakeoutSaaS.Infrastructure/App/Persistence/TakeoutAppDbContext.cs

@@ -807,10 +807,13 @@ public sealed class TakeoutAppDbContext(
         builder.Property(x => x.TenantId).IsRequired();
         builder.Property(x => x.Title).HasMaxLength(128).IsRequired();
         builder.Property(x => x.Content).HasColumnType("text").IsRequired();
-        builder.Property(x => x.AnnouncementType).HasConversion<int>();
-        builder.Property(x => x.PublisherScope).HasConversion<int>();
+        builder.Property(x => x.AnnouncementType)
+            .HasConversion<int>();
+        builder.Property(x => x.PublisherScope)
+            .HasConversion<int>();
         builder.Property(x => x.PublisherUserId);
-        builder.Property(x => x.Status).HasConversion<int>();
+        builder.Property(x => x.Status)
+            .HasConversion<int>();
         builder.Property(x => x.PublishedAt);
         builder.Property(x => x.RevokedAt);
         builder.Property(x => x.ScheduledPublishAt);
@@ -819,7 +822,9 @@ public sealed class TakeoutAppDbContext(
         builder.Property(x => x.Priority).IsRequired();
         builder.Property(x => x.IsActive).IsRequired();
         builder.Property(x => x.RowVersion)
-            .IsConcurrencyToken();
+            .IsRowVersion()
+            .IsConcurrencyToken()
+            .HasColumnType("bytea");
         ConfigureAuditableEntity(builder);
         ConfigureSoftDeleteEntity(builder);
         builder.HasIndex(x => new { x.TenantId, x.AnnouncementType, x.IsActive });