fix: Logo 从插件配置 API 动态获取

- img src 默认用静态 logo 路径
- footer.php 加 XHR 请求 config.json
- 读取 site_config.official_website_logo 动态替换

clientarea/hgcloud/login.php

@@ -17,7 +17,7 @@
   </div>
   <div class="template">
     <a href="/" class="back-home-link">
-      <img src="{$site_config.official_website_logo|default='/web/BlackFruit-web/assets/img/logo.png'}" alt="Logo" class="back-home-logo">
+      <img id="siteLogo" src="/web/BlackFruit-web/assets/img/logo.png" alt="Logo" class="back-home-logo">
     </a>
     <div id="login" v-cloak>
       <div class="login-container">