fix(backend): enumerate achievement types in some response schema (#15953)

* fix(backend): enumerate achievement types in some response schema

* refactor: use `ref`

packages/backend/src/models/json-schema/notification.ts

@@ -3,7 +3,6 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
-import { ACHIEVEMENT_TYPES } from '@/core/AchievementService.js';
 import { notificationTypes, userExportableEntities } from '@/types.js';
 
 const baseSchema = {
@@ -312,9 +311,7 @@ export const packedNotificationSchema = {
 				enum: ['achievementEarned'],
 			},
 			achievement: {
-				type: 'string',
-				optional: false, nullable: false,
-				enum: ACHIEVEMENT_TYPES,
+				ref: 'AchievementName',
 			},
 		},
 	}, {