fix: add missing OnModuleInit import in notifications service

backend/src/modules/notifications/notifications.service.ts

@@ -1,4 +1,4 @@
-import { Injectable, Logger } from '@nestjs/common';
+import { Injectable, Logger, OnModuleInit } from '@nestjs/common';
 import { ConfigService } from '@nestjs/config';
 import { InjectRepository } from '@nestjs/typeorm';
 import { In, Repository } from 'typeorm';