GitLab

- 新增 AnnouncementBell 组件，支持 Modal 弹窗和 Markdown 渲染
- 移除 Dashboard 横幅和独立公告页面
- 铃铛位置在 Header 文档按钮左侧，显示未读红点
- 支持点击查看详情、标记已读、全部已读等操作
- 完善国际化，移除所有硬编码中文
- 修复 AnnouncementTargetingEditor watch 循环问题

Implements announcements end-to-end (admin CRUD + read status, user list + mark read) with OR-of-AND targeting. Also breaks the ent<->service import cycle by moving schema-facing constants/targeting into a new domain package.