feat: 实现教师资料更新、操作日志和系统设置功能

新增教师资料更新功能，包括个人信息修改和密码更新
添加操作日志记录系统，记录用户关键操作
实现系统设置模块，支持动态配置系统参数
重构数据库模型，新增教师表和系统设置表
优化成绩录入逻辑，支持平时分、期中和期末成绩计算
添加数据导出功能，支持学生、教师和成绩数据导出
完善管理员后台，增加统计图表和操作日志查看

backend/models/Student.js

@@ -7,12 +7,33 @@ class Student {
     }
 
     static async create(studentData) {
-        const { id, name, className } = studentData;
+        const { id, name, class: className, major, grade, contact_info } = studentData;
         await db.query(
-            'INSERT INTO students (id, name, class) VALUES (?, ?, ?)',
-            [id, name, className]
+            'INSERT INTO students (id, name, class, major, grade, contact_info) VALUES (?, ?, ?, ?, ?, ?)',
+            [id, name, className, major, grade, contact_info]
         );
     }
+
+    static async update(id, data) {
+        const fields = [];
+        const values = [];
+        if (data.name) { fields.push('name = ?'); values.push(data.name); }
+        if (data.class) { fields.push('class = ?'); values.push(data.class); }
+        if (data.major !== undefined) { fields.push('major = ?'); values.push(data.major); }
+        if (data.grade !== undefined) { fields.push('grade = ?'); values.push(data.grade); }
+        if (data.contact_info !== undefined) { fields.push('contact_info = ?'); values.push(data.contact_info); }
+
+        if (fields.length === 0) return true;
+
+        values.push(id);
+        const sql = `UPDATE students SET ${fields.join(', ')} WHERE id = ?`;
+        await db.query(sql, values);
+        return true;
+    }
+
+    static async delete(id) {
+        await db.query('DELETE FROM students WHERE id = ?', [id]);
+    }
 }
 
-module.exports = Student;
+module.exports = Student;