完善建筑外观切换与宿主页面适配

src/components/explain/ExplainHallSelect.vue

@@ -1,6 +1,6 @@
 <template>
   <view class="explain-hall-select" :class="{ 'host-navigation': shouldUseHostNavigation }">
-    <view v-if="!shouldUseHostNavigation" class="explain-page-header">
+    <view v-if="showInternalHeader" class="explain-page-header">
       <view class="header-back" @tap="handleBack">
         <text class="header-back-icon">‹</text>
         <text class="header-back-text">返回</text>
@@ -241,6 +241,7 @@ const hallPreviewMap: Record<string, string> = {
 
 const filteredHalls = computed(() => props.halls)
 const shouldUseHostNavigation = computed(() => isEmbeddedInWechatMiniProgram())
+const showInternalHeader = computed(() => !shouldUseHostNavigation.value)
 const headerTitle = computed(() => {
   if (props.stage === 'unit') return props.selectedHallName || '选择业务单元'
   if (props.stage === 'stop') return props.selectedBusinessUnitName || '选择讲解点'