Introduce `.github/prompts/commit.prompt.md` as the contributor-facing description
of how assistants should stage, review, propose, and record commits.
- Document defaults: one file per commit, rare justified pairs, no blanket `git add`.
- Describe optional `.githooks/pre-commit` cap at two staged paths.
- Require reading the full `git diff --staged` (no truncation) before messaging.
- Spell out approval-before-commit flow and Conventional Commits subject lines.
- Scale the body to the patch: short summaries for small edits; large or
multi-concern diffs need grouped, substantive bullets so history stays readable.
- Keep checklist items aligned with that depth expectation.
Jukka Aho