Resolve merge conflicts and fix student course details functionality

backend/controllers/studentController.js

@@ -60,4 +60,4 @@ class StudentController {
     }
 }
 
-module.exports = StudentController;
+module.exports = StudentController;

backend/models/Course.js

@@ -39,4 +39,4 @@ class Course {
     }
 }
 
-module.exports = Course;
+module.exports = Course;

backend/services/studentService.js

@@ -1,6 +1,5 @@
 const Score = require('../models/Score');
 const Student = require('../models/Student');
-
 const Course = require('../models/Course');
 
 class StudentService {
@@ -23,10 +22,6 @@ class StudentService {
     }
 
     static async getStudentGrades(userId) {
-        // 先通过 userId 获取 studentId
-        // 假设 users.id = students.id，或者通过 user_id 关联
-        // 根据之前的 authService，我们假设 users.id 就是 students.id
-        
         // 确认学生是否存在
         const student = await Student.findById(userId);
         if (!student) {
@@ -72,4 +67,4 @@ class StudentService {
     }
 }
 
-module.exports = StudentService;
+module.exports = StudentService;