Add these four members to  src/notifications/enums/notification-type.enum.ts
(keep your existing members; just append):

  CHECKLIST_READY            = 'checklist_ready',
  CHECKLIST_DOC_UPLOADED     = 'checklist_doc_uploaded',
  CHECKLIST_CLIENT_SUBMITTED = 'checklist_client_submitted',
  CHECKLIST_REVIEW_RESULT    = 'checklist_review_result',

They are used by checklists.service.ts for:
  CHECKLIST_READY            → client bell: "Your audit checklist is ready"
  CHECKLIST_DOC_UPLOADED     → auditor bell: each client upload, real-time
  CHECKLIST_CLIENT_SUBMITTED → auditor bell: client pressed Submit
  CHECKLIST_REVIEW_RESULT    → client bell: approved / rejected summary