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.
- 新增 /purchase 页面（iframe + 新窗口兜底） - 管理员系统设置可配置开关与URL - 非 simple mode 才在侧边栏展示入口
ducky