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/models/Course.js

@@ -12,6 +12,31 @@ class Course {
         const rows = await db.query('SELECT * FROM courses WHERE id = ?', [id]);
         return rows[0];
     }
+
+    static async findDetailsById(id) {
+        const sql = `
+            SELECT c.*, u.name as teacher_name, cl.class_name
+            FROM courses c
+            JOIN users u ON c.teacher_id = u.id
+            JOIN classes cl ON c.class_id = cl.id
+            WHERE c.id = ?
+        `;
+        const rows = await db.query(sql, [id]);
+        return rows[0];
+    }
+
+    static async findByStudentId(studentId) {
+        const sql = `
+            SELECT c.*, u.name as teacher_name
+            FROM courses c
+            JOIN classes cl ON c.class_id = cl.id
+            JOIN students s ON cl.class_name = s.class
+            JOIN users u ON c.teacher_id = u.id
+            WHERE s.id = ?
+            ORDER BY c.course_code
+        `;
+        return await db.query(sql, [studentId]);
+    }
 }
 
 module.exports = Course;