feat(学生): 添加学生课程管理功能

- 新增我的课程页面及路由
- 实现课程列表和详情查看功能
- 更新导航链接指向新页面
- 添加成绩详情模态框
- 完善相关后端接口和服务

backend/routes/student.js

@@ -3,6 +3,8 @@ const router = express.Router();
 const StudentController = require('../controllers/studentController');
 const { requireAuth, requireRole } = require('../middleware/auth');
 
+router.get('/courses', requireAuth, requireRole(['student']), StudentController.getCourses);
+router.get('/courses/:id', requireAuth, requireRole(['student']), StudentController.getCourseDetails);
 router.get('/grades', requireAuth, requireRole(['student']), StudentController.getGrades);
 router.get('/grades/:id', requireAuth, requireRole(['student']), StudentController.getGradeDetails);