[kcempol]

Description

• Split ATSController into applicant, application-review, and recruitment services, with shared validation and formatting in ATSHelpers.
• Validate role ownership and save the profile, application, and applicant link in one MongoDB transaction.
• Persist stage follow-up work, serialize concurrent actions, resume failures with saved input, reconcile partial membership updates, and reuse onboarding invites.
• Preserve recruitment records during incomplete directory responses.
• Enable transactions in the local MongoDB stack and add code comments, a workflow explanation, and a testing guide.

Type of Change

• Bug fix
• New feature
• Refactor
• Chore / dependency update

Testing

• ./nx run pplserver:test: 247 passed, 0 failed, including 105 pre-refactor behavior comparisons and 14 MongoDB reliability tests.
• Generated HTTP routes are byte-identical to the original. API schemas are unchanged apart from corrected description text.
• git diff --check and changed shell-script syntax checks pass.
• Local stack passed all 17 service checks. Frontend/backend startup, HTTP responses, API proxy, and the original login-provider redirect were verified.
• Reviewed all 16 changed/new files for configured secrets; local environment files are ignored and excluded.

Review notes

• Submission requires a MongoDB replica set or sharded cluster. Existing local server settings need the documented MongoDB URL update.
• Stage retries are request-driven: repeat the same stage request. There is no automatic retry worker or dedicated UI retry button. SMTP delivery can still duplicate an email if a process stops between delivery and its completion checkpoint.
• Original S3 resumes are inaccessible to the team. Live resume upload/download and the complete browser submission flow remain unverified; tests use controlled storage responses. Local resume storage is not added here.
• Manual star ratings remain; AI resume scoring is not implemented in this PR.

Checklist

• Self-reviewed my own code
• No new console.log / debug statements left in
• Tested locally