feat: 添加学生个人中心页面和数据库备份功能

refactor(auth): 重构认证模块适配Bootstrap 5样式
feat(controller): 在登录响应中返回用户对象
feat(server): 添加学生个人中心路由
refactor(models): 重构学生和成绩模型结构
style: 更新登录和注册页面UI设计
chore: 添加数据库备份脚本和空备份文件

backend/models/Student.js

@@ -1,21 +1,16 @@
 const db = require('../config/database');
 
 class Student {
-    static async findByUserId(userId) {
-        const students = await db.query('SELECT * FROM students WHERE user_id = ?', [userId]);
-        return students[0];
-    }
-    
-    static async findById(studentId) {
-        const students = await db.query('SELECT * FROM students WHERE student_id = ?', [studentId]);
+    static async findById(id) {
+        const students = await db.query('SELECT * FROM students WHERE id = ?', [id]);
         return students[0];
     }
 
     static async create(studentData) {
-        const { id, name, className, userId } = studentData;
+        const { id, name, className } = studentData;
         await db.query(
-            'INSERT INTO students (id, name, class, user_id) VALUES (?, ?, ?, ?)',
-            [id, name, className, userId]
+            'INSERT INTO students (id, name, class) VALUES (?, ?, ?)',
+            [id, name, className]
         );
     }
 }