refactor: resolve remaining field audit issues

apps/server/src/entities/classroom-rental.entity.ts

@@ -11,6 +11,12 @@ import {
 import { Classroom } from './classroom.entity';
 import { Organization } from './organization.entity';
 
+export enum ClassroomRentalStatus {
+  ACTIVE = 'active',
+  ENDED = 'ended',
+  CANCELLED = 'cancelled',
+}
+
 @Entity('classroom_rentals')
 @Index(['classroomId', 'startDate', 'endDate'])
 export class ClassroomRental {
@@ -57,8 +63,8 @@ export class ClassroomRental {
   @Column({ name: 'total_amount', type: 'decimal', precision: 10, scale: 2, nullable: true })
   totalAmount: number;
 
-  @Column({ type: 'varchar', length: 20, default: 'active' })
-  status: string; // active / ended / cancelled
+  @Column({ type: 'varchar', length: 20, default: ClassroomRentalStatus.ACTIVE })
+  status: ClassroomRentalStatus | 'active' | 'ended' | 'cancelled';
 
   @Column({ type: 'text', nullable: true })
   notes: string;