refactor: resolve remaining field audit issues

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

@@ -1,4 +1,10 @@
-import { Entity, PrimaryGeneratedColumn, Column, CreateDateColumn, ManyToOne, JoinColumn } from 'typeorm';
+import { Entity, PrimaryGeneratedColumn, Column, CreateDateColumn } from 'typeorm';
+
+export enum ClassroomStatus {
+  AVAILABLE = 'available',
+  MAINTENANCE = 'maintenance',
+  ARCHIVED = 'archived',
+}
 
 @Entity('classrooms')
 export class Classroom {
@@ -20,14 +26,12 @@ export class Classroom {
   @Column({ name: 'room_type', type: 'varchar', length: 20, default: '大' })
   roomType: string; // 大 / 次大 / 小
 
-
-  @Column({ type: 'varchar', length: 20, default: 'reserved' })
-  status: string;
+  @Column({ type: 'varchar', length: 20, default: ClassroomStatus.AVAILABLE })
+  status: ClassroomStatus | 'available' | 'maintenance' | 'archived';
 
   @Column({ type: 'text', nullable: true })
   notes: string;
 
   @CreateDateColumn({ name: 'created_at' })
   createdAt: Date;
-
 }