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

@@ -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({