docs(contributing): document local checks matching CI gates

[lac1203]

Summary

• Documents local pre-submit checks that mirror blocking CI gates for contributors.
• Aligns the PR template checklist with the documented ruff, Windows-footgun, and test checks.
• Keeps this contributor-facing guidance separate from post-merge verification and visual QA workflows.

Verification

python - <<'PY'
from pathlib import Path
c=Path('CONTRIBUTING.md').read_text()
pr=Path('.github/PULL_REQUEST_TEMPLATE.md').read_text()
for s in ['ruff check .','check-windows-footguns.py --diff main','pytest']:
    assert s in c or s in pr, s
print('contributor validation docs sanity OK')
PY

Claude reported validating the documented commands against the repo workflows; no code, secrets, deploys, or merges.

[teknium1]

Thanks for improving the contributor pre-submit guidance. The gap is real: current CONTRIBUTING.md:944-949 lists only test/manual/platform/scope checks, and .github/PULL_REQUEST_TEMPLATE.md:49 still asks only for pytest.

Problems

• The proposed “exact match” is inaccurate for the Windows check: CI runs python scripts/check-windows-footguns.py --all in .github/workflows/lint.yml:160, while the new guidance uses --diff main.
• The text also says these are the blocking checks for every PR. A .github/ edit enables every lane in scripts/ci/classify_changes.py:82-88, and the required aggregate covers additional lanes in .github/workflows/ci.yml:137-166.

Suggested changes

• Use --all for an exact CI-equivalent footgun command, or label --diff main as a faster local preflight.
• Narrow the claim to applicable Python checks rather than all required gates.

This is an automated hermes-sweeper review.