feat(shadcn): allow removal of variables from external registries

[bcorbold]

Allows external registries to remove CSS / tailwind variables that are not being used by their systems

Use case

We are building out our component registry for internal use but have chosen to use our own named tokens for theming

Currently, if we wanted to remove the defaults, that requires a manual step for our consumers to delete those CSS variables/tailwind colours manually after running shadcn init.

We've worked around this temporarily by having our own cli that calls shadcn init and removes those variables

Proposal

Update schemas/utils to allow null when defining cssVariables or in the tailwind properties to remove them when running shadcn add .... This should allow us to remove our own cli to fully leverage the shadcn tooling 🎉

// http://localhost:3000/registry/theme-foo.json
{
  "theme": "theme-foo",
  "type": "registry:theme",
  "cssVars": {
    "light": {
      "card": null,
      "card-foreground": null,
      "info": "210.8 100% 56.9%"
    },
    "dark": {
      "card": null,
      "card-foreground": null
    }
  },
  "tailwind": {
    "config": {
      "theme": {
        "extend": {
          "colors": {
            "card": null,
            "info": "hsl(var(--info))"
          }
        }
      }
    }
  }
}

After running pnpx shadcn@latest add http://localhost:3000/registry/theme-foo.json this should:

1. Remove --card, and --card-foreground from the globals.css file
2. Add --info to the globals.css file
3. Remove theme.extend.colors.card from tailwind.config.ts
4. Add theme.extend.colors.info to tailwind.config.ts

[vercel]

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

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