fix: @entity(...) decorator gefixt in backend/src/entities

backend/src/entities/content/attachment.entity.ts

@@ -1,7 +1,8 @@
 import { Entity, ManyToOne, PrimaryKey, Property } from '@mikro-orm/core';
 import { LearningObject } from './learning-object.entity.js';
+import { AttachmentRepository } from '../../data/content/attachment-repository.js';
 
-@Entity()
+@Entity({ repository: () => AttachmentRepository })
 export class Attachment {
     @ManyToOne({ entity: () => LearningObject, primary: true })
     learningObject!: LearningObject;