[codex] link public demo review runner

[InfoSecHack]

Summary

• Link the local-only public demo review runner from docs/START_HERE.md.
• Add a short runner section to docs/REVIEWER_GUIDE.md.
• Point both entry docs to docs/case-studies/public-demo-review-runbook.md.

Boundaries

• Docs-only change.
• No live AWS, Terraform, AWS CLI, STS, Lambda API, or iam:PassRole calls.
• No new evidence claims, reasoner changes, benchmark semantic changes, composite scoring, or pass/fail benchmark label.

Validation

• grep -nEi 'run the local demo review|run_public_demo_review.py|summary.md|manifest.json|path-overcounting-uncertainty-groups.json|local-only|public-demo-review-runbook' docs/START_HERE.md docs/REVIEWER_GUIDE.md
• grep -RInE '[0-9]{12}' docs tests | grep -v '000000000000' || true
• grep -RInE 'arn:aws:iam::[0-9]{12}' docs tests | grep -v '000000000000' || true
• ind . -name 'result.json' -o -name 'terraform.tfstate*' -o -name '.terraform.lock.hcl' -o -name '*.tfplan' -o -name 'terraform-outputs.json'
• ./scripts/check.sh
• ./scripts/test_fast.sh
• git diff --check