[Monorepo] Decide where a definition of done lives for PRs #1124

Summary

.github/pull_request_template.md has Summary, Changes proposed, Context for reviewers, and Additional information. There is no definition of done checklist, so nothing prompts an author to confirm tests, docs, or a changeset before review.

The open question is whether the PR template is the right home for this. Each section of the repo has a different set of things that need to be done as part of a PR, so a single universal checklist may not work. Alternatives worth considering include per-area checklists, CODEOWNERS-driven guidance, or automated checks that enforce the same things without relying on the author.

Open questions

1. Is a universal definition of done achievable across the repo's sections, or does it need to vary by area?
2. Is the PR template the right place, or is this better handled by automation or per-area docs?
3. Which items genuinely need author confirmation versus a CI check?

Acceptance criteria

• A recommendation is recorded on this ticket and agreed with the team
• The agreed approach is implemented and renders or runs correctly on a new PR