[INTW26] Add shortlist columns to applicant records

[dqvidl]

Notion ticket link

Update Applicant Records Database to Support Shortlisting

Implementation description

• Add two boolean columns to ApplicantRecord (isShortlistedForInterview, isShortlistedForOffer), default false. Migration adds them to applicant_records and removes them in down.

Steps to test

1. Run docker exec recruitment_tools_backend node migrate up and confirm it runs without error.
2. In pgAdmin, check applicant_records: columns isShortlistedForInterview and isShortlistedForOffer exist, type boolean, default false.

What should reviewers focus on?

• Migration up/down and that the model matches the new columns.

Checklist

• My PR name is descriptive and in imperative tense
• My commit messages are descriptive and in imperative tense. My commits are atomic and trivial commits are squashed or fixup'd into non-trivial commits
• I have run the appropriate linter(s)
• I have requested a review from the PL, as well as other devs who have background knowledge on this PR or who will be building on top of this PR