Design System — Onboarding + Shared Brand Tokens

The design-system skill is the shared brand owner for the markdown-html plugin. Run its onboarding once. Every converter (md-document, md-review, md-slides) reads the resulting config via config_loader.py and applies the same 12 CSS custom properties to its output. Without this, conversions render with placeholder defaults — technically functional but unbranded.

This skill ships exactly three Python tools:

1. onboard.py — interactive (or --defaults / --set / --show / --reset) wizard.
2. config_loader.py — importable customization loader with project > global > defaults precedence and MARKDOWN_HTML_NO_CONFIG=1 bypass.
3. brand_palette_validator.py — WCAG-AA contrast checker + HSL palette deriver.

All three are stdlib-only and contain no LLM calls (deterministic per Path-B discipline).

When to invoke