feat(日历组件): 添加课程筛选状态持久化功能

在可折叠日历组件中增加 sessionStorage 存储功能，用于保存用户选择的课程筛选状态
添加状态恢复逻辑和列表变化监听，确保筛选状态与数据同步

 <!--
  * @Date: 2025-01-25 15:34:17
  * @LastEditors: hookehuyr hookehuyr@gmail.com
- * @LastEditTime: 2025-12-18 22:33:09
+ * @LastEditTime: 2025-12-18 23:23:57
  * @FilePath: /mlaj/src/components/ui/CollapsibleCalendar.vue
  * @Description: 可折叠日历组件
 -->
@@ -156,6 +156,27 @@ const selectedCourseText = ref('全部作业')
 const selectedCourseId = ref('')
 const showRulesPopup = ref(false)
 
+// 存储键名
+const STORAGE_KEY = 'collapsible_calendar_filter_state'
+// 是否已恢复状态
+const isRestored = ref(false)
+
+// 尝试从 sessionStorage 恢复状态
+try {
+    const savedState = sessionStorage.getItem(STORAGE_KEY)
+    if (savedState) {
+        const { selectedCourseId: savedId, selectedCourseText: savedText } = JSON.parse(savedState)
+        // 只有当保存的值存在时才恢复 (savedId 可以是空字符串，表示全部作业)
+        if (savedId !== undefined) {
+            selectedCourseId.value = savedId
+            selectedCourseText.value = savedText || '全部作业'
+            isRestored.value = true
+        }
+    }
+} catch (e) {
+    console.error('Failed to restore calendar filter', e)
+}
+
 const { y } = useScroll(window)
 const isHeaderHidden = ref(false)
 const lastY = ref(0)
@@ -258,8 +279,36 @@ const onConfirmCourse = (result) => {
     selectedCourseId.value = option.value
     showCoursePicker.value = false
     emit('select-course', option.value)
+
+    // 保存状态
+    sessionStorage.setItem(STORAGE_KEY, JSON.stringify({
+        selectedCourseId: selectedCourseId.value,
+        selectedCourseText: selectedCourseText.value
+    }))
 }
 
+// 监听 subtaskList 变化，用于在恢复状态后同步筛选
+watch(() => props.subtaskList, (newList) => {
+    if (newList && newList.length > 0 && isRestored.value) {
+        // 尝试在列表中找到对应的项，更新文本
+        const target = newList.find(item => item.id === selectedCourseId.value)
+
+        if (target) {
+            selectedCourseText.value = target.title
+        } else if (selectedCourseId.value) {
+            // 如果有ID但在列表中找不到（可能是作业被删除），则重置为全部
+            selectedCourseId.value = ''
+            selectedCourseText.value = '全部作业'
+        }
+
+        // 通知父组件筛选变更，确保数据与筛选状态一致
+        emit('select-course', selectedCourseId.value)
+
+        // 重置标记，确保只执行一次
+        isRestored.value = false
+    }
+}, { immediate: true })
+
 // 计算属性：格式化当前日期显示
 const formattedCurrentDate = computed(() => {
     return dayjs(currentDate.value).format('YYYY年MM月DD日')