feat(学生): 添加成绩分析功能及密码修改功能

- 新增成绩分析页面，包含GPA趋势图、成绩分布图和学分进度
- 实现学生密码修改功能，包括前端表单和后端验证逻辑
- 添加课程类别分析功能，展示不同类别课程的GPA表现
- 优化学生仪表板和课程页面导航链接
- 增加数据加载状态提示和错误处理

backend/server.js

@@ -99,6 +99,9 @@ app.get('/student/dashboard', requirePageAuth, requirePageRole(['student']), (re
 app.get('/student/my-courses', requirePageAuth, requirePageRole(['student']), (req, res) => {
     res.sendFile(path.join(__dirname, '../frontend/views/student/my_courses.html'));
 });
+app.get('/student/grade-analysis', requirePageAuth, requirePageRole(['student']), (req, res) => {
+    res.sendFile(path.join(__dirname, '../frontend/views/student/grade_analysis.html'));
+});
 app.get('/student/profile', requirePageAuth, requirePageRole(['student']), (req, res) => {
     res.sendFile(path.join(__dirname, '../frontend/views/student/profile.html'));
 });