fix(课程页面): 修复课程目录滚动容器引用错误并优化代码格式

修复StudyDetailPage中滚动容器引用未定义的问题，添加正确的ref引用
移除CourseDetailPage中多余的空行，保持代码整洁

@@ -269,7 +269,7 @@ const toggleFavorite = async () => {
 // Curriculum items
 const curriculumItems = computed(() => {
   if (!course.value) return [];
-  
+
   return [
     { title: '课程特色', active: activeTab.value === '课程特色', show: !!course.value.feature },
     { title: '课程大纲', active: activeTab.value === '课程大纲', show: !!(course.value.schedule && course.value.schedule.length > 0) },
@@ -368,13 +368,13 @@ onMounted(async () => {
       isFavorite.value = foundCourse.is_favorite;
       isPurchased.value = foundCourse.is_buy;
       isReviewed.value = foundCourse.is_comment;
-      
+
       // 设置默认选中的 tab，确保选中的 tab 有内容
       const availableTabs = curriculumItems.value;
       if (availableTabs.length > 0 && !availableTabs.some(item => item.title === activeTab.value)) {
         activeTab.value = availableTabs[0].title;
       }
-      
+
       // 获取评论列表
       await fetchCommentList()
     } else {

@@ -215,7 +215,7 @@
                 </div>
 
                 <!-- 可滚动的目录列表 -->
-                <div class="flex-1 overflow-y-auto px-4 py-2">
+                <div ref="scrollContainer" class="flex-1 overflow-y-auto px-4 py-2" style="overflow-y: scroll;">
                     <div v-if="course_lessons.length" class="space-y-4">
                         <div v-for="(lesson, index) in course_lessons" :key="index" @click="handleLessonClick(lesson)"
                             class="bg-white p-4 cursor-pointer hover:bg-gray-50 transition-colors border-b border-gray-200 relative">
@@ -252,7 +252,7 @@ import dayjs from 'dayjs';
 import { formatDate } from '@/utils/tools'
 import axios from 'axios';
 import { v4 as uuidv4 } from "uuid";
-
+import { useIntersectionObserver } from '@vueuse/core';
 import PdfPreview from '@/components/ui/PdfPreview.vue';
 
 // 导入接口
@@ -272,6 +272,8 @@ const audioPlayerRef = ref(null);
 const showCommentPopup = ref(false);
 const popupComment = ref('');
 
+const scrollContainer = ref(null);
+
 // 课程目录相关
 const course_lessons = ref([]);
 const course_type_maps = ref({
@@ -870,7 +872,7 @@ watch(showCatalog, (newVal) => {
                     const lessonTop = selectedLesson.offsetTop;
                     const lessonHeight = selectedLesson.clientHeight;
                     const scrollTop = lessonTop - (containerHeight / 2) + (lessonHeight / 2);
-                    
+
                     // 平滑滚动到指定位置
                     scrollContainer.scrollTo({
                         top: scrollTop,