PRs that omit Fixes #N break the release-time reverse lookup
(issue → closing PR → merge sha → first containing tag), since the
auto-link only fires on the explicit closing keywords. We've been doing
this by hand on recent fixes; codify it so future PRs don't drift.
- Add .github/pull_request_template.md with a Fixes # placeholder so
the link surface is in front of the author by default.
- Add a corresponding bullet to the Bug follow-up workflow in the root
AGENTS.md so the discipline lives next to the methodology that
produces issue-linked work.
