Add a strict "evidence bar" section to CONTRIBUTING.md and a PR template
that force every contribution to prove a human exercised the change:
a human-written why, a live before/after evidence block, DCO sign-off,
and a scope statement. Enumerate auto-closed categories (ETHOS edits,
voice/YC cleanup, generated-file-only diffs, blind-AI-sweep PRs). CI
enforcement (changeset-required, DCO check, generated-file guard) is
documented as the next step tied to the Changesets migration rather than
built speculatively.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
