Add shared React UI package

[brxs]

Summary

• add the independently publishable, MIT-licensed @protocol-works/ui workspace package
• extract the established portable primitives and typography contracts from the protocol.works website into 26 direct subpath exports
• keep Next.js, Tauri, theme persistence, and product-specific visual recipes in their consuming applications
• ship Tailwind v4 source registration and nested light/dark/accent/signal surface recipes
• extend CI with TypeScript builds, SSR catalogue coverage, package-boundary checks, real Tailwind utility discovery, and npm tarball verification

This is the shared foundation for migrating the website and Rabbithole without flattening Rabbithole's musical/instrument-specific controls. Those controls remain local adapters or variants on top of these primitives.

Supports Symbients/llm-orchestrator#222.

Verification

• npm run check
• npm pack --dry-run
• npm pack --dry-run --workspace @protocol-works/ui

After merge, publish with npm publish --workspace @protocol-works/ui; the manifest is configured for public access.