The pre-commit hooks lack the issue-reference, traction and contributors checks that make lint runs #1276

Where: .pre-commit-config.yaml, Makefile (lint).

Current gap: make lint runs check_issue_refs.py, check_traction.py and check_contributors.py; the pre-commit config has hooks for the em-dash, link, explainer-count and explainer-structure checks and ruff, so a commit can pass the hooks and fail make lint.

Suggested approach: Add hooks for the three checks (restricted to the files they read, and tolerant of a missing gh as the scripts already are).

Done when: editing ROADMAP.md, METRICS.md, README.md or CONTRIBUTORS.md runs the matching hook.