feat(plan-governance): add audit, approval, rollback, and drift controls

[Delqhi]

Scope

Add packaging, test, and release scaffolding so the redesign stays reproducible.

Build requirements

• tests/ for CLI / validator / templates
• GitHub Actions workflow for lint, test, build, and artifacts
• matrix execution for current supported Python versions
• Makefile and release workflow
• optional SARIF output artifact support

Acceptance criteria

• PRs fail when the package or tests break
• CI uses the same commands intended for local use
• build artifacts are reproducible