feat: 会员中心全局暗色主题重构

阶段一：全局覆盖
- 新增 dark-override.css (450+ 行)，覆盖所有 Element UI 组件暗色样式
  - 输入框、表格、Tabs、弹窗、按钮、分页、复选框、下拉框等
  - 侧边栏、顶栏、主内容区暗色背景
  - 滚动条、日期选择器、消息面板等
- header.php 引入 dark-override.css

阶段二：页面独立 CSS 暗色化（22 个文件）
- 白色背景 #fff → #161b22
- 浅灰背景 #F3F5F9 → #0d1117
- 深色文字 #171725/#1E2736 → #E6E8EB
- 灰色文字 #8692B0 → #8B949E
- 浅色边框 #E6E7EB → rgba(255,255,255,0.06)
- 悬停背景 #F5F7FA → #21262d

clientarea/hgcloud/css/agreement.css

@@ -4,7 +4,7 @@
   padding: 0.2rem 3rem;
 }
 .contnet-right-out .content-right {
-  border: 1px solid #e6e7eb;
+  border: 1px solid rgba(255,255,255,0.06);
   border-radius: 3px;
   padding: 0.36rem 0.5rem;
   overflow-x: auto;
@@ -13,7 +13,7 @@
   font-size: 0.28rem;
   font-weight: bold;
   line-height: 0.28rem;
-  color: #1e2736;
+  color: #E6E8EB;
 }
 .contnet-right-out .content-right .right-keywords-time {
   display: flex;
@@ -22,7 +22,7 @@
 .contnet-right-out .content-right .right-keywords-time .right-time,
 .contnet-right-out .content-right .right-keywords-time .right-keywords {
   font-size: 0.14rem;
-  color: #8692b0;
+  color: #8B949E;
   margin-top: 0.14rem;
 }
 .contnet-right-out .content-right .right-keywords-time .right-keywords {