feat(announcements): add admin/user announcement system

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.

frontend/src/api/admin/announcements.ts

@@ -0,0 +1,71 @@
+/**
+ * Admin Announcements API endpoints
+ */
+
+import { apiClient } from '../client'
+import type {
+  Announcement,
+  AnnouncementUserReadStatus,
+  BasePaginationResponse,
+  CreateAnnouncementRequest,
+  UpdateAnnouncementRequest
+} from '@/types'
+
+export async function list(
+  page: number = 1,
+  pageSize: number = 20,
+  filters?: {
+    status?: string
+    search?: string
+  }
+): Promise<BasePaginationResponse<Announcement>> {
+  const { data } = await apiClient.get<BasePaginationResponse<Announcement>>('/admin/announcements', {
+    params: { page, page_size: pageSize, ...filters }
+  })
+  return data
+}
+
+export async function getById(id: number): Promise<Announcement> {
+  const { data } = await apiClient.get<Announcement>(`/admin/announcements/${id}`)
+  return data
+}
+
+export async function create(request: CreateAnnouncementRequest): Promise<Announcement> {
+  const { data } = await apiClient.post<Announcement>('/admin/announcements', request)
+  return data
+}
+
+export async function update(id: number, request: UpdateAnnouncementRequest): Promise<Announcement> {
+  const { data } = await apiClient.put<Announcement>(`/admin/announcements/${id}`, request)
+  return data
+}
+
+export async function deleteAnnouncement(id: number): Promise<{ message: string }> {
+  const { data } = await apiClient.delete<{ message: string }>(`/admin/announcements/${id}`)
+  return data
+}
+
+export async function getReadStatus(
+  id: number,
+  page: number = 1,
+  pageSize: number = 20,
+  search: string = ''
+): Promise<BasePaginationResponse<AnnouncementUserReadStatus>> {
+  const { data } = await apiClient.get<BasePaginationResponse<AnnouncementUserReadStatus>>(
+    `/admin/announcements/${id}/read-status`,
+    { params: { page, page_size: pageSize, search } }
+  )
+  return data
+}
+
+const announcementsAPI = {
+  list,
+  getById,
+  create,
+  update,
+  delete: deleteAnnouncement,
+  getReadStatus
+}
+
+export default announcementsAPI
+