feat: add department_id to all business entities

apps/server/src/entities/occupancy.entity.ts

@@ -9,6 +9,7 @@ import {
 import { Student } from './student.entity';
 import { Room } from './room.entity';
 import { Tenant } from './tenant.entity';
+import { Department } from './department.entity';
 
 @Entity('occupancies')
 export class Occupancy {
@@ -59,4 +60,11 @@ export class Occupancy {
   @ManyToOne(() => Room, (r) => r.occupancies)
   @JoinColumn({ name: 'room_id' })
   room: Room;
+
+  @Column({ name: 'department_id', type: 'integer', nullable: true })
+  departmentId: number;
+
+  @ManyToOne(() => Department, { nullable: true })
+  @JoinColumn({ name: 'department_id' })
+  department: Department;
 }