fix(teacher/checkinPage): 修复年级和班级切换时课程值未重置的问题

在切换年级或班级时，重置课程选择值以避免数据不一致

 <!--
   * @Date: 2025-05-29 15:34:17
  * @LastEditors: hookehuyr hookehuyr@gmail.com
- * @LastEditTime: 2025-06-26 11:22:30
+ * @LastEditTime: 2025-06-27 15:09:17
  * @FilePath: /mlaj/src/views/teacher/checkinPage.vue
   * @Description: 文件描述
 -->
@@ -9,7 +9,7 @@
   <AppLayout :hasTitle="false">
     <van-config-provider :theme-vars="themeVars">
       <van-sticky>
-        <van-dropdown-menu active-color="#4caf50">
+        <van-dropdown-menu active-color="#4caf50" swipe-threshold="2">
           <van-dropdown-item v-model="selectGradeValue" :options="gradeOption" @change="handleGradeChange" />
           <van-dropdown-item v-model="selectClassValue" :options="classOption" @change="handleClassChange" />
           <van-dropdown-item v-model="selectCourseValue" :options="courseOption" @change="handleCourseChange" />
@@ -213,6 +213,7 @@ const courseOption = ref([]);
 const handleGradeChange = async (val) => {
   console.log('val', val);
   selectGradeValue.value = val;
+  selectCourseValue.value = null;
   // 根据年级ID 更新过滤列表
   getFilterList(val);
   // 重置分页参数
@@ -226,6 +227,7 @@ const handleGradeChange = async (val) => {
 const handleClassChange = (val) => {
   console.log('val', val);
   selectClassValue.value = val;
+  selectCourseValue.value = null;
   // 根据年级ID和班级ID 更新过滤列表
   getFilterList(selectGradeValue.value, val);
   // 重置分页参数