Merge branch 'feat/service-layer' into feat/service-layer-adriaan

# Conflicts:
#	backend/src/controllers/classes.ts
#	backend/src/controllers/students.ts
#	backend/src/data/users/teacher-repository.ts
#	backend/src/interfaces/assignment.ts
#	backend/src/interfaces/teacher.ts
#	backend/src/routes/classes.ts
#	backend/src/services/assignments.ts
#	backend/src/services/class.ts
#	backend/src/services/students.ts
#	backend/src/util/translation-helper.ts

backend/src/interfaces/class.ts

@@ -0,0 +1,25 @@
+import { Class } from "../entities/classes/class.entity.js";
+
+export interface ClassDTO {
+    id: string;
+    displayName: string;
+    teachers: string[];
+    students: string[];
+    joinRequests: string[];
+    endpoints?: {
+        self: string;
+        invitations: string;
+        assignments: string;
+        students: string;
+    };
+}
+
+export function mapToClassDTO(cls: Class): ClassDTO {
+    return {
+        id: cls.classId,
+        displayName: cls.displayName,
+        teachers: cls.teachers.map(teacher => teacher.username),
+        students: cls.students.map(student => student.username),
+        joinRequests: [], // TODO
+    }
+};