fix: 评估日期选择器联动，天数自动计算日期或手动选日期

app/templates/student.html

@@ -889,6 +889,22 @@ async function loadGoalOptions() {
     document.getElementById('assign-start-date').value = new Date().toISOString().split('T')[0];
 }
 
+// 评估日期联动：选择天数后自动计算日期，或直接选日期
+document.getElementById('assign-assessment-days').addEventListener('change', function() {
+    const days = parseInt(this.value);
+    if (days) {
+        const d = new Date();
+        d.setDate(d.getDate() + days);
+        document.getElementById('assign-assessment-date').value = d.toISOString().split('T')[0];
+    }
+});
+
+document.getElementById('assign-assessment-date').addEventListener('change', function() {
+    if (this.value) {
+        document.getElementById('assign-assessment-days').value = '';
+    }
+});
+
 document.getElementById('confirm-assign-goal').addEventListener('click', async () => {
     const goalId = document.getElementById('assign-goal-select').value;
     const assessmentDays = document.getElementById('assign-assessment-days').value;