修复业务单元返回栈重复页面

- 业务单元列表上一页为首页讲解 Tab 时直接按页面栈返回
- 保留独立讲解展厅列表页的正常返回逻辑
- 避免返回时插入内容重复的讲解展厅列表页

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/pages/explain/business-unit-list.vue

@@ -109,7 +109,10 @@ const handleBack = () => {
   const pages = getCurrentPages()
   const previousPage = pages.length >= 2 ? pages[pages.length - 2] : null
 
-  if (previousPage?.route === 'pages/explain/list') {
+  if (
+    previousPage?.route === 'pages/explain/list'
+    || previousPage?.route === 'pages/index/index'
+  ) {
     uni.navigateBack({
       delta: 1,
       fail: goBackToExplainHallList