feat(首页): 公告不再只放置顶那条，改成最新三条（置顶的排最前、带标），右边写发布日期

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/web/src/oj/home/dashboard.vue

@@ -149,10 +149,10 @@ async function loadSubmissions() {
   submissions.value = res.results
 }
 
-/** 首页只放置顶的公告（用户定的），其余从顶栏「公告」进 */
+/** 首页放前三条公告（后端置顶在前、再按发布时间），其余从顶栏「公告」进 */
 async function loadAnnouncements() {
-  const res = await getAnnouncementList(0, 10)
+  const res = await getAnnouncementList(0, 3)
-  announcements.value = res.results.filter((item) => item.top)
+  announcements.value = res.results
 }
 
 async function loadKnowledge() {
@@ -524,20 +524,24 @@ async function openAnnouncement(item: AnnouncementListItem) {
           </router-link>
         </n-card>
 
-        <!-- 公告只放置顶的；别的从顶栏「公告」进 -->
+        <n-card v-if="announcements.length" title="公告" :bordered="false" class="card">
+          <template #header-extra>
+            <router-link to="/announcement" class="more">全部</router-link>
+          </template>
           <div
             v-for="item in announcements"
             :key="item.id"
-          class="card pinned"
+            class="row clickable"
             role="button"
             tabindex="0"
             @click="openAnnouncement(item)"
             @keyup.enter="openAnnouncement(item)"
           >
-          <n-tag type="warning" size="small" :bordered="false">置顶</n-tag>
+            <n-tag v-if="item.top" type="warning" size="small" :bordered="false">置顶</n-tag>
             <span class="row-title">{{ item.title }}</span>
-          <router-link to="/announcement" class="more" @click.stop>公告 →</router-link>
+            <n-text depth="3" class="row-meta">{{ dateText(item.createTime) }}</n-text>
           </div>
+        </n-card>
       </div>
     </div>
 
@@ -581,14 +585,6 @@ async function openAnnouncement(item: AnnouncementListItem) {
   padding-top: 12px;
 }
 
-.pinned {
-  display: flex;
-  align-items: center;
-  gap: 10px;
-  padding: 14px 18px;
-  cursor: pointer;
-}
-
 .grid {
   display: grid;
   grid-template-columns: minmax(0, 3fr) minmax(0, 2fr);