fix: use hardcoded Chinese text for announcement option label

- Replace i18n reference with hardcoded '发公告' for announcement option
- Ensure consistent display of announcement feature for admin users

Author: jiazengp

src/components/forum/ForumLocalNav.vue

@@ -69,7 +69,7 @@ const selectPublishTopicMenu = computed(() => {
   // 为管理员添加发公告选项
   if (isAdmin.value) {
     baseItems.push({
-      label: message.value.forum.labels.ann,
+      label: '发公告',
       icon: 'i-lucide-megaphone',
       action: () => {
         location.hash = 'PUBLISH-TOPIC-ANN'