feat(distribution): 公告中心支持分站自定义

公告中心（前台公告列表/详情）此前完全没有站点概念，分站访客只能看到主站公告。
本次按「默认继承主站、站长可切仅本站」的口径支持分站自定义。

数据与口径：
- 新增 announcements.distribution_site_id（0=主站），前台按站点隔离
- 新增 distribution_sites.announcement_mode：inherit（默认，主站+本站）/ own_only（仅本站）

后端：
- 公告模块新增 ResolvePublicSiteScope：主站 [0]、inherit [0, siteID]、own_only [siteID]，
  站点编码无效/已停用回落主站；列表与详情都按该范围过滤，详情不再允许跨站按 ID 读取
- 管理端公告列表支持按站点筛选（site_id：不传=全部，0=主站，>0=分站）并带出站点名
- 分销模块新增本站公告 CRUD（distribution/announcement.go）：强制 distribution_site_id=本站，
  先过 ensureSiteAccess，跨站更新/删除/上下架一律 ErrAnnouncementNotFound
- UpdateSiteBranding 支持 announcement_mode 切换（非法值报错，读侧非法历史值回落 inherit）
- 新增权限 distribution:announcement_view|manage 并授予 super_admin/ops/finance，
  站长开通时继承 ops 角色即自动获得
- 路由：站长侧 /api/distribution/announcements*，平台侧 /api/admin/distribution/announcements*

前端：
- 分销后台新增「公告中心」页：来源开关（继承主站+本站 / 仅本站）、本站公告列表与
  新建/编辑/发布/下架/归档/恢复/删除，空态按来源模式给出引导
- 平台后台公告页新增「站点」列与筛选，新建公告可选择归属站点（主站或指定分站代发）
- 前台 PC/移动无需改动：请求已带 X-Distribution-Site-Code，后端按站点隔离，页面已有空态

测试：
- 公告模块：主站/继承/仅本站三种可见范围、跨站详情拦截、无效站点回落、管理端站点筛选
- 分销模块：本站公告 CRUD 与跨站防护、公告来源开关校验与非法值容错

frontend/src/features/admin/api/adminAnnouncements.ts

@@ -3,6 +3,8 @@ import type { ApiResponse } from '@/shared/types/types'
 import type { Announcement, PaginatedResult } from '@/features/announcement/api/announcements'
 
 export interface CreateAnnouncementRequest {
+  /** 归属站点：0（默认）=主站，>0=分站代发 */
+  distribution_site_id?: number
   title: string
   content: string
   category: 'notice' | 'tutorial' | 'rule' | 'faq'
@@ -23,6 +25,8 @@ export interface UpdateAnnouncementRequest {
 export async function fetchAdminAnnouncements(params: {
   status?: string
   category?: string
+  /** 站点筛选：不传=全部，0=主站，>0=指定分站 */
+  site_id?: number
   page?: number
   page_size?: number
 }): Promise<PaginatedResult<Announcement>> {

frontend/src/features/admin/components/AnnouncementDialog.vue

@@ -15,6 +15,10 @@ import type {
   CreateAnnouncementRequest,
   UpdateAnnouncementRequest,
 } from '@/features/admin/api/adminAnnouncements'
+import {
+  fetchDistributionSites,
+  type DistributionSite,
+} from '@/features/admin/api/adminDistribution'
 import { uploadAdminFile } from '@/shared/api/files'
 import { debugError } from '@/shared/utils/debug'
 import { readError } from '@/shared/utils/error'
@@ -44,6 +48,7 @@ const imageSettingsForm = ref({
   useCustomWidth: true,
 })
 const formData = ref<CreateAnnouncementRequest>({
+  distribution_site_id: 0,
   title: '',
   content: '',
   category: 'notice',
@@ -52,6 +57,26 @@ const formData = ref<CreateAnnouncementRequest>({
   is_important: false,
 })
 
+// 站点列表：0=主站（默认），其余为分站；公告归属站点只在新建时可选。
+const distributionSites = ref<DistributionSite[]>([])
+const currentSiteLabel = computed(() => {
+  if (props.mode === 'create') return ''
+  if (!props.announcement?.distribution_site_id) return '主站'
+  const matched = distributionSites.value.find(
+    item => item.id === props.announcement?.distribution_site_id
+  )
+  return matched ? `${matched.site_name}（${matched.site_code}）` : '分站'
+})
+
+async function loadDistributionSites() {
+  if (distributionSites.value.length > 0) return
+  try {
+    distributionSites.value = await fetchDistributionSites()
+  } catch (error) {
+    debugError('加载分销站点失败', error)
+  }
+}
+
 const categories = [
   { value: 'notice', label: '通知公告', icon: Bell },
   { value: 'tutorial', label: '使用教程', icon: Document },
@@ -86,6 +111,7 @@ watch(
     if (val) {
       if (props.mode === 'edit' && props.announcement) {
         formData.value = {
+          distribution_site_id: props.announcement.distribution_site_id,
           title: props.announcement.title,
           content: props.announcement.content,
           category: props.announcement.category as any,
@@ -95,6 +121,7 @@ watch(
         }
       } else {
         formData.value = {
+          distribution_site_id: 0,
           title: '',
           content: '',
           category: 'notice',
@@ -103,6 +130,7 @@ watch(
           is_important: false,
         }
       }
+      void loadDistributionSites()
       formRef.value?.clearValidate()
     }
   }
@@ -278,6 +306,23 @@ function escapeMarkdownImageText(text: string) {
 <template>
   <el-dialog :model-value="visible" :title="dialogTitle" width="800px" @close="handleClose">
     <el-form ref="formRef" :model="formData" :rules="rules" label-width="100px">
+      <el-form-item label="归属站点">
+        <el-select
+          v-if="mode === 'create'"
+          v-model="formData.distribution_site_id"
+          placeholder="选择公告归属站点"
+        >
+          <el-option :value="0" label="主站" />
+          <el-option
+            v-for="site in distributionSites"
+            :key="site.id"
+            :value="site.id"
+            :label="`${site.site_name}（${site.site_code}）`"
+          />
+        </el-select>
+        <el-tag v-else effect="plain">{{ currentSiteLabel }}</el-tag>
+      </el-form-item>
+
       <el-form-item label="公告标题" prop="title">
         <el-input
           v-model="formData.title"

frontend/src/features/admin/views/AdminAnnouncementsView.vue

@@ -23,6 +23,10 @@ import {
   type CreateAnnouncementRequest,
   type UpdateAnnouncementRequest,
 } from '@/features/admin/api/adminAnnouncements'
+import {
+  fetchDistributionSites,
+  type DistributionSite,
+} from '@/features/admin/api/adminDistribution'
 import type { Announcement } from '@/features/announcement'
 import { formatDateTime } from '@/shared/utils/time'
 import AnnouncementDialog from '../components/AnnouncementDialog.vue'
@@ -35,6 +39,9 @@ const currentPageSize = ref(20)
 const total = ref(0)
 const statusFilter = ref('')
 const categoryFilter = ref('')
+// 站点筛选：'' = 全部，0 = 主站，>0 = 指定分站
+const siteFilter = ref<number | ''>('')
+const distributionSites = ref<DistributionSite[]>([])
 
 const dialogVisible = ref(false)
 const dialogMode = ref<'create' | 'edit'>('create')
@@ -54,7 +61,23 @@ const statusOptions = [
   { value: 'archived', label: '已归档' },
 ]
 
-onMounted(loadAnnouncements)
+onMounted(() => {
+  void loadDistributionSites()
+  void loadAnnouncements()
+})
+
+async function loadDistributionSites() {
+  try {
+    distributionSites.value = await fetchDistributionSites()
+  } catch {
+    distributionSites.value = []
+  }
+}
+
+function siteLabel(row: Announcement): string {
+  if (!row.distribution_site_id) return '主站'
+  return row.distribution_site_name || `分站 #${row.distribution_site_id}`
+}
 
 async function loadAnnouncements() {
   loading.value = true
@@ -62,6 +85,7 @@ async function loadAnnouncements() {
     const result = await fetchAdminAnnouncements({
       status: statusFilter.value || undefined,
       category: categoryFilter.value || undefined,
+      site_id: siteFilter.value === '' ? undefined : Number(siteFilter.value),
       page: currentPage.value,
       page_size: currentPageSize.value,
     })
@@ -222,6 +246,22 @@ function getStatusType(status: string): '' | 'success' | 'info' | 'warning' {
     </div>
 
     <div class="filter-bar">
+      <el-select
+        v-model="siteFilter"
+        placeholder="筛选站点"
+        clearable
+        @change="handleFilterChange"
+        style="width: 170px"
+      >
+        <el-option label="全部站点" :value="''" />
+        <el-option label="主站" :value="0" />
+        <el-option
+          v-for="site in distributionSites"
+          :key="site.id"
+          :value="site.id"
+          :label="`${site.site_name}（${site.site_code}）`"
+        />
+      </el-select>
       <el-select
         v-model="statusFilter"
         placeholder="筛选状态"
@@ -272,6 +312,14 @@ function getStatusType(status: string): '' | 'success' | 'info' | 'warning' {
             </div>
           </template>
         </el-table-column>
+        <el-table-column label="站点" width="150">
+          <template #default="{ row }">
+            <el-tag v-if="row.distribution_site_id" type="success" effect="plain" size="small">
+              {{ siteLabel(row) }}
+            </el-tag>
+            <el-tag v-else type="info" effect="plain" size="small">主站</el-tag>
+          </template>
+        </el-table-column>
         <el-table-column label="分类" width="120">
           <template #default="{ row }">
             <el-tag

frontend/src/features/announcement/api/announcements.ts

@@ -3,6 +3,10 @@ import type { ApiResponse } from '@/shared/types/types'
 
 export interface Announcement {
   id: number
+  /** 归属站点：0=主站，>0=分站 */
+  distribution_site_id: number
+  /** 管理端列表带出的站点名（前台不返回） */
+  distribution_site_name?: string
   title: string
   content: string
   category: string