fix(teacher/formPage): 初始化周期选择默认值

确保表单加载时自动设置周期选择的默认值

@@ -945,6 +945,10 @@ onMounted(async () => {
       value: String(value) // 确保值为字符串类型
     }));
 
+    // 初始化周期选择
+    formData.value.cycle_text = cycleOptions.value[0].text;
+    formData.value.cycle = cycleOptions.value[0].value;
+
     // 处理作业类型数据
     if (data.task_attachment_type) {
       attachmentTypeOptions.value = Object.entries(data.task_attachment_type).map(([key, value]) => ({