Bot: squash-merge signatures so old forks can be merged

[geetxnshgoyal]

Bug

The bot couldn't merge #53: Resource not accessible by integration.

Cause: #53's fork was made before the workflow changes on main. A merge commit from that fork would bring those workflow changes in, and GitHub doesn't let GITHUB_TOKEN write workflow files. #56, forked after the last workflow change, merged fine, and that matches.

Fix

merge_method: "squash": a single new commit on top of main containing only the student's signature, however old their fork is. The student is still the commit author, and history stays one commit per signature.

After merging

Close and reopen #53 (a re-run replays the old workflow). The bot should then merge it.

This PR's own check fails by design (it isn't a signature), so it needs an admin merge.

[github-actions]

Hi @geetxnshgoyal 👋 thanks for signing the workbook! The check found a problem:

• Your file must be named exactly signatures/geetxnshgoyal.md — your GitHub username, capitals included. Yours is .github/workflows/validate-signature.yml. Fix it with: git mv ".github/workflows/validate-signature.yml" signatures/geetxnshgoyal.md

How to fix it (in your clone, on the same branch as this PR):

# fix the file as described above, then:
git add -A
git commit -m "Fix signature"
git push

Your file should look like:

# Your Real Name

- **GitHub:** @geetxnshgoyal
- **Batch:** 2026
- **I'm here to:** your own line
- **One thing I've built:** a link, or nothing yet

Push to this same PR. Don't open a new one. This comment updates itself each time the check re-runs.