feat(announcement): 新增首页弹窗公告功能并完成弹窗UI视觉重构

- 数据库与后端：announcements 表增加 is_popup 字段及迁移脚本，提供前台弹窗接口与多公告优先级选取，补全选优单测
- 管理后台：总后台与分销后台公告编辑新增「弹窗公告」开关与列表标签展示
- 前台交互：前台 PC/移动端首页引入 AnnouncementPopup，支持同一用户同一天同一公告仅弹一次的关闭记录
- 视觉优化：重构弹窗结构，顶栏镶嵌品牌橙流光细条与浅暖橙通知徽标，中间内嵌浅灰舒适阅读卡片，底部搭配大锤橙实心主操作按钮
- 验证方式：后端 announcement 单测通过，前端 npm run build 编译无报错，浏览器实机截图验证

frontend/src/features/listings/views/HomeView.vue

@@ -13,6 +13,7 @@ import {
   type HomeBannerSlide,
 } from '@/features/listings/api/homeConfig'
 import { ElMessage } from 'element-plus'
+import AnnouncementPopup from '@/features/announcement/components/AnnouncementPopup.vue'
 import AuthImage from '@/shared/components/business/AuthImage.vue'
 import {
   emptyListingPublishOptions,
@@ -497,6 +498,9 @@ if (!restored) {
   <section class="pc-home-redesign">
     <HomeAnnouncement :announcements="displayAnnouncements" />
 
+    <!-- 弹窗公告：进入首页弹出，必须手动关闭，同一天同一条只弹一次 -->
+    <AnnouncementPopup />
+
     <main class="home-content">
       <!-- 商城专属标识 Banner -->
       <div v-if="siteStore.isDistribution" class="dist-portal-banner">

frontend/src/features/listings/views/MobileHomeView.vue

@@ -24,6 +24,7 @@ import {
   type HomeBannerSlide,
 } from '@/features/listings/api/homeConfig'
 import { showToast } from 'vant'
+import AnnouncementPopup from '@/features/announcement/components/AnnouncementPopup.vue'
 import AuthImage from '@/shared/components/business/AuthImage.vue'
 import MobileHomeFilterSheet, { type FilterSection } from './MobileHomeFilterSheet.vue'
 import {
@@ -795,6 +796,8 @@ if (!restoreHomeConfigFromCache()) {
 
 <template>
   <main class="mobile-shell">
+    <!-- 弹窗公告：进入首页弹出，必须手动关闭，同一天同一条只弹一次 -->
+    <AnnouncementPopup />
     <div ref="scrollEl" class="mobile-scroll" @scroll.passive="handleListScroll">
       <!-- ========== Hero 区域：顶部搜索与公告 ========== -->
       <section class="mobile-hero">