Add pre-planning design contract generation and post-execution visual audit
for frontend phases. Closes the gap where execute-phase runs without a visual
contract, producing inconsistent spacing, color, and typography across components.
New agents: gsd-ui-researcher (UI-SPEC.md), gsd-ui-checker (6-dimension
validation), gsd-ui-auditor (6-pillar scored audit + registry re-vetting).
Third-party shadcn registry blocks are machine-vetted at contract time,
verification time, and audit time — three enforcement points, not a checkbox.
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
