Set up pre-commit hooks with secret detection

[braboj]

Summary

No pre-commit hooks exist. This violates base/quality-gates.md Layer 2 MUSTs. No secret detection (gitleaks or equivalent) at any layer.

Deliverables

• Install husky + lint-staged (or equivalent)
• Add gitleaks or similar secret detection to pre-commit
• Optionally add Markdown lint and Astro check to pre-commit
• Document in PLAYBOOK.md

Found by

360-degree analysis (Quality category), 2026-04-29.