fix(ui): 修复移动端数据加载显示

- 为 topic-card-list 添加 v-if 条件渲染
- 添加空状态提示
- 增强调试信息（console.log）
- 确保移动端卡片列表正确显示

platform/frontend/topics.html

@@ -143,7 +143,7 @@
                             </el-table-column>
                         </el-table>
                         <!-- 移动端卡片列表 -->
-                        <div class="topic-card-list">
+                        <div class="topic-card-list" v-if="filteredTopics && filteredTopics.length > 0">
                             <div v-for="topic in filteredTopics" :key="topic.id" class="topic-card">
                                 <div class="topic-card-header">
                                     <div class="topic-card-title">{{ topic.title }}</div>
@@ -185,12 +185,20 @@
         const TopicsApp = {
             data() { return { isLoggedIn: false, isAdmin: false, currentUser: { username: '' }, topics: [], filterStatus: '', selectedTopicIds: [], loadingTable: false } },
             computed: {
-                filteredTopics() { if (!this.topics.length) return []; if (!this.filterStatus) return this.topics; return this.topics.filter(t => t.status === this.filterStatus); },
+                filteredTopics() { 
+                    console.log('[DEBUG] filteredTopics called, filterStatus:', this.filterStatus, 'topics count:', this.topics.length); 
+                    if (!this.topics.length) { console.log('[DEBUG] topics is empty'); return []; } 
+                    if (!this.filterStatus) { console.log('[DEBUG] no filter, return all'); return this.topics; } 
+                    const result = this.topics.filter(t => t.status === this.filterStatus); 
+                    console.log('[DEBUG] filtered result count:', result.length); 
+                    return result; 
+                },
                 countByStatus() { return (status) => this.topics.filter(t => t.status === status).length; }
             },
             methods: {
                 async fetchTopics() {
                     this.loadingTable = true;
+                    console.log('[DEBUG] fetchTopics called');
                     try {
                         const token = localStorage.getItem('authToken');
                         const response = await fetch('/api/topics', { headers: { 'Authorization': 'Bearer ' + token } });