feat: add department_id to all business entities

apps/server/src/entities/personal-expense.entity.ts

@@ -7,6 +7,7 @@ import {
   JoinColumn,
 } from 'typeorm';
 import { Student } from './student.entity';
+import { Department } from './department.entity';
 
 @Entity('personal_expenses')
 export class PersonalExpense {
@@ -40,4 +41,11 @@ export class PersonalExpense {
   @ManyToOne(() => Student, (s) => s.personalExpenses)
   @JoinColumn({ name: 'student_id' })
   student: Student;
+
+  @Column({ name: 'department_id', type: 'integer', nullable: true })
+  departmentId: number;
+
+  @ManyToOne(() => Department, { nullable: true })
+  @JoinColumn({ name: 'department_id' })
+  department: Department;
 }