fix(settings): 移除设置中心的客户端下载入口

右上角导航已有客户端下载按钮，设置中心重复展示无必要

frontend/app.html

@@ -2488,21 +2488,6 @@
           <p class="settings-page-subtitle">管理存储策略、主题外观与账号安全</p>
         </div>
 
-        <h3 class="settings-section-title" style="margin-bottom: 20px;">
-          <i class="fas fa-desktop"></i> 客户端下载
-        </h3>
-        <div class="settings-panel" style="background: var(--bg-card); padding: 20px; border-radius: 12px; border: 1px solid var(--glass-border); margin-bottom: 30px;">
-          <div style="display: flex; justify-content: space-between; align-items: center; gap: 12px; flex-wrap: wrap;">
-            <div style="color: var(--text-secondary); font-size: 13px;">
-              下载最新版桌面客户端（Windows x64）
-            </div>
-            <button class="btn btn-primary" :disabled="desktopClientDownloading" @click="downloadDesktopClient">
-              <i :class="desktopClientDownloading ? 'fas fa-spinner fa-spin' : 'fas fa-download'"></i>
-              {{ desktopClientDownloading ? '获取安装包...' : '下载桌面客户端' }}
-            </button>
-          </div>
-        </div>
-
         <!-- 存储管理 - 仅用户可选择 -->
         <div v-if="user && !user.is_admin && storagePermission === 'user_choice'" class="settings-section settings-storage-choice" style="margin-bottom: 40px;">
           <h3 class="settings-section-title" style="margin-bottom: 20px;">