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/Migrations/20251225090000_AddTenantAnnouncementRowVersionTrigger.cs

@@ -0,0 +1,50 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace TakeoutSaaS.Infrastructure.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddTenantAnnouncementRowVersionTrigger : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.Sql(
+                """
+                CREATE OR REPLACE FUNCTION public.set_tenant_announcement_row_version()
+                RETURNS trigger AS $$
+                BEGIN
+                    NEW."RowVersion" = decode(md5(random()::text || clock_timestamp()::text), 'hex');
+                    RETURN NEW;
+                END;
+                $$ LANGUAGE plpgsql;
+                """);
+
+            migrationBuilder.Sql(
+                """
+                DROP TRIGGER IF EXISTS trg_tenant_announcements_row_version ON tenant_announcements;
+                CREATE TRIGGER trg_tenant_announcements_row_version
+                BEFORE INSERT OR UPDATE ON tenant_announcements
+                FOR EACH ROW EXECUTE FUNCTION public.set_tenant_announcement_row_version();
+                """);
+
+            migrationBuilder.Sql(
+                """
+                UPDATE tenant_announcements
+                SET "RowVersion" = decode(md5(random()::text || clock_timestamp()::text), 'hex')
+                WHERE "RowVersion" IS NULL OR octet_length("RowVersion") = 0;
+                """);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.Sql(
+                """
+                DROP TRIGGER IF EXISTS trg_tenant_announcements_row_version ON tenant_announcements;
+                DROP FUNCTION IF EXISTS public.set_tenant_announcement_row_version();
+                """);
+        }
+    }
+}