fix: vervang v4 naar 6 char class id

backend/src/entities/classes/class.entity.ts

@@ -1,15 +1,18 @@
 import { Collection, Entity, ManyToMany, PrimaryKey, Property } from '@mikro-orm/core';
-import { v4 } from 'uuid';
 import { Teacher } from '../users/teacher.entity.js';
 import { Student } from '../users/student.entity.js';
 import { ClassRepository } from '../../data/classes/class-repository.js';
+import { customAlphabet } from "nanoid";
+
+const generateClassId = customAlphabet('ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789', 6);
+
 
 @Entity({
     repository: () => ClassRepository,
 })
 export class Class {
     @PrimaryKey()
-    classId? = v4();
+    classId? = generateClassId();
 
     @Property({ type: 'string' })
     displayName!: string;