style(survey): 修改 AI 洞察背景样式

- 移除 AI 洞察卡片的图片背景
- 添加从浅蓝色到白色的线性渐变背景

src/views/Survey/views/Analysis/Index.vue

@@ -103,7 +103,7 @@ onUnmounted(() => {
   // width: 100%;
 
   .ai-insight {
-    background-image: url('@/assets/img/home/item-back.png');
+    background: linear-gradient(to bottom, rgb(239, 249, 252) 0, white 20%);
     background-position: 11% 11%;
 
     .ai-insight-content {