🚀 Feature: --mode migrate should prompt for the base

[JoshuaKGoldberg]

Bug Report Checklist

• I have pulled the latest main branch of the repository.
• I have searched for related issues and found none that matched my issue.

Overview

Splitting out of #1355: running npx create-typescript-app --mode migrate doesn't explicitly call out what the inferred --base is on. You can only see it by looking at the rerun suggestion.

●  Tip: to run again with the same input values, use: npx create-typescript-app --mode migrate --base minimum --access public --author danvk --description "Code samples that scale" --directory literate-ts --email-github [email protected] --email-npm [email protected] --mode migrate --owner danvk --repository literate-ts --title "Literate TS"

...but that leads to broken expectations when the inferred base doesn't match what the user would expect. And if it defaults to --base minimum, that's a lot of missing functionality!

Migration should prompt the user for the --base. I was surprised to see it default to minimum.

Additional Info

Co-authored-by: @danvk