refactor(frontend): ActivityPoster 移入 pages/activity 子包，主包减重

- components/ActivityPoster.vue → pages/activity/components/ActivityPoster.vue
- 唯一消费方 pages/activity/activity-detail/activity-detail.vue 的 import 改为
  @/pages/activity/components/ActivityPoster.vue
- 组件内只有 @/utils/format.js、@/utils/fontScale.js 两处别名引用，移动后无需改动
- 校验：verify-vue-compile 两个文件 模板/样式/脚本 均通过；全仓无残留旧路径引用

cfc-frontend/pages/activity/activity-detail/activity-detail.vue

@@ -326,7 +326,7 @@ import { getActivityDetail, activityCheckin, cancelActivityRegistration, createA
 import config from '@/config.js'
 import shareMixin from '../../../components/share-mixin.js'
 import MpHtml from '@/components/mp-html/mp-html.vue'
-import ActivityPoster from '@/components/ActivityPoster.vue'
+import ActivityPoster from '@/pages/activity/components/ActivityPoster.vue'
 import RelatedContent from '@/components/RelatedContent.vue'
 import { backfillProfile } from '../../../utils/profile-backfill.js'
 import { parseDate } from '@/utils/format.js'