feat(registry): add @materialcn to the registry directory

[guillermo-rebolledo]

Adds @materialcn to apps/v4/registry/directory.json.

materialcn is Material 3 Expressive for shadcn/ui: Base UI primitives restyled with M3 tokens extracted from the official Material 3 Design Kit .fig, rather than transcribed from the docs site.

The load-bearing idea is that shadcn components are never patched for color — their semantic variables (--primary, --card, --border) are pointed at M3 roles, so stock shadcn markup renders as Material. That means the token layer ships as one item, and adding it alone rethemes an existing shadcn project without taking any components:

npx shadcn add @materialcn/materialcn-theme

• Registry: https://guillermo-rebolledo.github.io/materialcn/r/registry.json
• Source: https://github.com/guillermo-rebolledo/materialcn (MIT)
• 66 items — 57 components plus the theme and its supporting libraries.

Checks

• pnpm validate:registries passes.
• The registry is public, flat, and served over HTTPS; registry.json carries no inlined file content.
• Verified end to end with shadcn add by URL and by namespace into scratch projects, which typecheck clean afterwards.

[vercel]

@guillermo-rebolledo is attempting to deploy a commit to the shadcn-pro Team on Vercel.

A member of the Team first needs to authorize it.

[shadcn]

Thanks, added this to #11861. Closing this one so we can track it there.