feat(课程页面): 添加课程目录滚动位置记忆功能

实现从课程详情页返回时恢复滚动位置的功能
添加数据属性标记课程目录项
新增滚动状态存储和恢复相关方法

@@ -56,7 +56,7 @@
                     <div class="text-gray-700 text-sm leading-relaxed" v-html="course?.learning_goal"></div>
                     <br />
                 </div>
-                <van-empty v-if="!course?.feature && !course?.highlights && course?.learning_goal" description="暂无详情" />
+                <van-empty v-else description="暂无详情" />
             </div>
 
             <div class="h-2 bg-gray-100"></div>
@@ -64,6 +64,7 @@
             <div id="catalog" class="py-4">
                 <div v-if="course_lessons.length" class="space-y-4">
                     <div v-for="(lesson, index) in course_lessons" :key="index"
+                        :data-lesson-id="lesson.id"
                         @click="goToStudyDetail(lesson.id)"
                         class="bg-white p-4 cursor-pointer hover:bg-gray-50 transition-colors border-b border-gray-200 relative">
                         <div class="text-black text-base font-medium mb-2">{{ lesson.title }}</div>
@@ -257,6 +258,94 @@ const course_type_maps = ref({
 const task_list = ref([]);
 const timeout_task_list = ref([]);
 
+/**
+ * 生成课程滚动状态存储键
+ * @returns {string} 滚动状态存储键
+ * 注释：用于在会话存储中保存和恢复课程目录滚动位置
+ */
+
+const get_scroll_store_key = () => {
+    const course_id = router.currentRoute.value.params.id || '';
+    return `study_course_scroll_${course_id}`;
+};
+
+/**
+ * 判断是否需要恢复滚动位置
+ * @returns {boolean} 是否需要恢复滚动
+ * 注释：根据历史状态判断是否从课程详情页返回
+ */
+
+const should_restore_scroll = () => {
+    const forward = window.history && window.history.state ? window.history.state.forward : null;
+    if (!forward) return false;
+    return String(forward).includes('studyDetail');
+};
+
+/**
+ * 保存当前滚动位置
+ * @param {string} lesson_id - 当前课程目录项ID
+ * 注释：在用户滚动到目录项时调用，记录滚动位置和目录项ID
+ */
+
+const save_scroll_state = (lesson_id) => {
+    const key = get_scroll_store_key();
+    const payload = {
+        scroll_y: window.scrollY || 0,
+        lesson_id: lesson_id || '',
+        saved_at: Date.now(),
+    };
+    sessionStorage.setItem(key, JSON.stringify(payload));
+};
+
+/**
+ * 滚动到指定目录项
+ * @param {string} lesson_id - 目标目录项ID
+ * @returns {boolean} 是否成功滚动
+ * 注释：根据目录项ID找到元素并滚动到其位置，考虑顶部导航栏高度
+ */
+
+const scroll_to_lesson = (lesson_id) => {
+    if (!lesson_id) return false;
+    const el = document.querySelector(`[data-lesson-id="${lesson_id}"]`);
+    if (!el) return false;
+    const rect = el.getBoundingClientRect();
+    const buffer = 10;
+    const offset_top = (tabs_wrapper_height.value || 0) + buffer;
+    const top_offset = Math.max(0, rect.top + window.scrollY - offset_top);
+    window.scrollTo({ top: top_offset, left: 0, behavior: 'auto' });
+    return true;
+};
+
+/**
+ * 恢复滚动位置
+ * @returns {void}
+ * 注释：在组件挂载时调用，根据存储状态滚动到上次记录位置
+ */
+
+const restore_scroll_state = async () => {
+    if (!should_restore_scroll()) return;
+    const key = get_scroll_store_key();
+    const raw = sessionStorage.getItem(key);
+    if (!raw) return;
+
+    let state = null;
+    try {
+        state = JSON.parse(raw);
+    } catch (e) {
+        sessionStorage.removeItem(key);
+        return;
+    }
+
+    await nextTick();
+    await new Promise((resolve) => requestAnimationFrame(() => requestAnimationFrame(resolve)));
+
+    const restored = scroll_to_lesson(state.lesson_id);
+    if (!restored && typeof state.scroll_y === 'number') {
+        window.scrollTo({ top: state.scroll_y, left: 0, behavior: 'auto' });
+    }
+    sessionStorage.removeItem(key);
+};
+
 onMounted(async () => {
     /**
      * 组件挂载时获取课程详情
@@ -292,6 +381,8 @@ onMounted(async () => {
     // 初始化标签容器宽度监听
     initTabsContainerWidth();
     handleScroll();
+    // 恢复滚动位置
+    restore_scroll_state();
 });
 
 // 在组件卸载时移除监听器
@@ -393,6 +484,7 @@ const handleTabChange = (name) => {
 };
 
 const goToStudyDetail = (lessonId) => {
+    save_scroll_state(lessonId);
     router.push(`/studyDetail/${lessonId}`);
 };