fix: 今日新增筛选filteredTopics未处理'today'导致始终为空，状态筛选改为全量拉取保统计准确

- filteredTopics 对 filterStatus='today' 直接返回 this.topics（服务器已按日期过滤），避免按不存在的 status 再次过滤导致空列表
- fetchTopics 改为只有 'today' 走服务端 ?today=true；其他状态仍然全量拉取后客户端过滤，保证 statusStats 统计按钮数字准确
- 保留 watch 移除（用户能自由清除筛选）

platform/frontend/topics.html

@@ -190,7 +190,7 @@ const TopicsApp = {
     },
     computed: {
         filteredTopics() {
-            if (!this.filterStatus) return this.topics;
+            if (!this.filterStatus || this.filterStatus === 'today') return this.topics;
             const map = { 'pending': ['pending','待处理'], 'review': ['review','待审查'], 'ready': ['ready','待发布'], 'published': ['published','已发布'] };
             const allowed = map[this.filterStatus] || [this.filterStatus];
             return this.topics.filter(t => allowed.includes(t.status));
@@ -235,16 +235,9 @@ const TopicsApp = {
         async fetchTopics() {
             this.loadingTable = true;
             try {
-                const params = new URLSearchParams();
-                if (this.filterStatus === 'today') {
-                    params.set('today', 'true');
-                } else if (this.filterStatus) {
-                    params.set('status', this.filterStatus);
-                }
-                const qs = params.toString();
-                const data = await this.api('/api/topics' + (qs ? '?' + qs : ''));
+                const params = this.filterStatus === 'today' ? '?today=true' : '';
+                const data = await this.api('/api/topics' + params);
                 this.topics = data || [];
-                if (qs) this.$message.success(`加载 ${this.filterStatus} 选题成功`);
             } catch (error) {
                 console.error('获取选题失败:', error);
                 this.$message.error(`获取选题失败: ${error.message}`);