fix: 实现空间 TotalReads 统计，修复 selectMention 闭包

- P0-2: posts/show.html selectMention 闭包 var→let 修复
- P0-3: GetUserStats 增加 SUM(views_count) 统计，替换硬编码 int64(0)
- 更新 Fix_List.md 标注 P0-1/2/3 已修复

templates/MetaLab-2026/html/posts/show.html

@@ -934,8 +934,8 @@
         dropdown.style.left = (rect.left + window.scrollX) + 'px';
         dropdown.style.width = Math.max(rect.width, 200) + 'px';
 
-        for (var i = 0; i < users.length; i++) {
-            var u = users[i];
+        for (let i = 0; i < users.length; i++) {
+            let u = users[i];
             var item = document.createElement('div');
             item.className = 'mention-item';
             item.innerHTML = '<span class="mention-username">' + escapeHtml(u.username) + '</span><span class="mention-uid">' + escapeHtml(u.uid) + '</span>';