Add diff_has_code_files() and ci_required_for_pr() helpers to
ci-helpers.sh. Non-code PRs (docs/*, formulas/*, evidence/*, *.md)
that have no CI results now skip the CI gate instead of being stuck
forever.
Applied to:
- review-pr.sh: CI gate skipped for non-code PRs
- review-poll.sh: CI gate skipped for non-code PRs
- dev-poll.sh: CI state treated as "success" for non-code PRs in
orphan, stuck-PR, and backlog merge paths
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>