feat: add exam score management

apps/server/src/entities/exam-score.entity.ts

@@ -9,12 +9,20 @@ import {
 } from 'typeorm';
 import { Student } from './student.entity';
 import { StudentEnrollment } from './student-enrollment.entity';
+import { Exam } from './exam.entity';
 
 @Entity('exam_scores')
 export class ExamScore {
   @PrimaryGeneratedColumn()
   id: number;
 
+  @Column({ name: 'exam_id', type: 'integer', nullable: true })
+  examId: number | null;
+
+  @ManyToOne(() => Exam, (exam) => exam.scores, { nullable: true, onDelete: 'CASCADE' })
+  @JoinColumn({ name: 'exam_id' })
+  exam: Exam | null;
+
   @Column({ name: 'student_id', type: 'integer' })
   studentId: number;
 
@@ -39,13 +47,13 @@ export class ExamScore {
   subject: string;
 
   @Column({ type: 'decimal', precision: 5, scale: 2, nullable: true })
-  score: number;
+  score: number | null;
 
   @Column({ name: 'class_avg', type: 'decimal', precision: 5, scale: 2, nullable: true })
-  classAvg: number;
+  classAvg: number | null;
 
   @Column({ type: 'integer', nullable: true })
-  rank: number;
+  rank: number | null;
 
   @Column({ name: 'exam_date', type: 'date', nullable: true })
   examDate: string;