style: 登录注册左上角改为 Logo（替代返回首页文字）

- 左上角显示网站 Logo 图片，点击回首页
- 默认 70% 透明度，悬停变 100%
- 删除箭头 SVG 和文字

clientarea/hgcloud/css/regist.css

@@ -411,7 +411,7 @@
   }
 }
 
-/* ---- 返回首页按钮 ---- */
+/* ---- 左上角 Logo ---- */
 .back-home-link {
   position: fixed;
   top: 24px;
@@ -419,21 +419,23 @@
   z-index: 20;
   display: flex;
   align-items: center;
-  gap: 6px;
-  color: rgba(139, 148, 158, 0.6);
   text-decoration: none;
-  font-size: 13px;
-  padding: 6px 12px;
-  border-radius: 6px;
+  padding: 6px;
+  border-radius: 8px;
   transition: all 0.2s;
 }
 
 .back-home-link:hover {
-  color: #FFFFFF;
   background: rgba(255, 255, 255, 0.05);
 }
 
-.back-home-link svg {
-  width: 16px;
-  height: 16px;
+.back-home-logo {
+  height: 28px;
+  width: auto;
+  opacity: 0.7;
+  transition: opacity 0.2s;
+}
+
+.back-home-link:hover .back-home-logo {
+  opacity: 1;
 }