fix: 修复访客视图 PostCount 字段引用错误

- 访客视图 .SpaceUser.PostCount -> .PostCount，与 Owner 视图保持一致
- PostCount 由 Controller 作为顶层字段传入，不在 SpaceUser 对象中

templates/MetaLab-2026/html/space/index.html

@@ -96,7 +96,7 @@
                class="space-tab{{if eq .ActiveTab "articles"}} active{{end}}">
                 <svg viewBox="0 0 24 24" width="16" height="16"><path fill="currentColor" d="M14 2H6c-1.1 0-2 .9-2 2v16c0 1.1.9 2 2 2h12c1.1 0 2-.9 2-2V8l-6-6zM6 20V4h7v5h5v11H6z"/></svg>
                 文章
-                <span class="tab-count">{{.SpaceUser.PostCount}}</span>
+                <span class="tab-count">{{.PostCount}}</span>
             </a>
             <a href="/space/{{.SpaceUser.ID}}?tab=following"
                class="space-tab{{if or (eq .ActiveTab "following") (eq .ActiveTab "followers")}} active{{end}}">