test: cover maintenance window monitor edits

[sanmaxdev]

Summary

• add a real-Mongo regression test for editing a maintenance window's monitor membership
• verify removed monitors no longer match the window
• verify kept and newly added monitors both resolve back to the edited window

Context

Refs #3551. The service layer already maps the edit payload's monitors field to monitorIds; this adds repository-level coverage so the Mongo persistence path is locked down too.

Test Plan

• TMPDIR=/home/ubuntu/tmp npm test -- --runTestsByPath test/integration/maintenanceWindowRepository.test.ts test/unit/services/maintenanceWindowService.test.ts --runInBand
• npx prettier --check test/integration/maintenanceWindowRepository.test.ts
• npm run build