Short theme presets, like shadcn's b0

A style or a theme encodes as a three-character code, u00 and up, and grows only when you leave the curated set. Named presets live in the registry as map-themes, so an app installs them once and passes MAP_THEMES.boreal.

• npx shadcn add @unmap/map-themes installs named constants for the styles and the eight theme presets
• The create page's export dialog offers three next steps: new project, existing project, and the code itself