feat(footer): 页脚新增管理面板入口链接（moderator+可见）

chore: 站点名称保持硬编码 MetaLab，后台移除该设置项，恢复 Nav 双拼样式
       site.brand 后端逻辑保留，页脚仍可配置

templates/admin/html/site-settings/index.html

@@ -8,16 +8,6 @@
         <div class="settings-section">
             <div class="section-title">基本设置</div>
             <div class="section-body">
-                <div class="setting-item">
-                    <div class="setting-info">
-                        <span class="setting-label">品牌名称</span>
-                        <span class="setting-desc">显示在页面标题、页脚、管理面板中</span>
-                    </div>
-                    <div class="setting-input-wrap">
-                        <input type="text" id="setting-site-brand" class="setting-input" placeholder="MetaLab" value="{{.Brand}}">
-                        <button class="btn btn-sm btn-primary btn-save" data-key="site.brand" data-input="setting-site-brand">保存</button>
-                    </div>
-                </div>
                 <div class="setting-item">
                     <div class="setting-info">
                         <span class="setting-label">版权信息</span>