Align ~ alias to components.json in custom registries

[iloveitaly]

I love the new custom registry functionality. I've been getting it working with this project:

nainglinnkhant/lingua-time#3

One of the issues I've run into is ~ does not represent the same path as what is defined in the components JSON.

For instance:

• In my project it represents the ~/web/app folder when used in a tsx (as defined by components.json)
• Within the registry.json the ~ seems to reference the root level folder, i.e. the ~/web folder in this case.

This means in order to get the components to clone into the ~/app/components folder, I need to hard code the app sub-directory in the target field on the registry JSON. This doesn't work because not all projects will use the app folder. Some use src, etc.

It would be great if:

1. shadcn used app/ as the ~ (as defined in the components + tsconfig)
2. shadcn allowed the user to customize the ~ path on a per-command basis (shadcn add --clone=use/this/dir). One use case here is having a dedicated folder for all non-official components that you're cloning: shadcn add --clone=app/components/vendor