feat(about): 添加背景图片并优化样式

为移动端和网页端的关于页面添加背景图片，同时调整z-index和背景样式以提升视觉效果

app/pages/mobile/about.vue

@@ -163,6 +163,9 @@ const togglecard = (index) => {
       box-shadow: 0 4px 4px 0 rgba(98, 0, 255, 0.30) inset;
       backdrop-filter: blur(7px);
       padding: 16px;
+      z-index: 2;
+      background: url('/images/about/text-bg.png') no-repeat center;
+      background-size:cover;
 
       .mb-about-box-text {
         color: #FFF;

app/pages/web/about.vue

@@ -96,10 +96,12 @@ useHead({
       height: 487px;
       margin-top: 192px;
       border-radius: 30px;
-      border: 1px solid rgba(13, 0, 34, 0.00);
       background: linear-gradient(179deg, rgba(3, 0, 20, 0.50) 1.22%, rgba(151, 87, 255, 0.10) 41.19%);
       box-shadow: 0 4px 4px 0 rgba(98, 0, 255, 0.30) inset;
       backdrop-filter: blur(25px);
+      z-index: 2;
+      background: url('/images/about/text-bg.png') no-repeat center;
+      background-size: cover;
 
       .about-box-text {
         width: 520px;