Add shadcn/UI as UI framework

[jacob-leger]

I was testing to see if this boilerplate was right for my Next.js project. I use ShadCN/UI for almost all my projects, and I wished to see that as a possibility with SuperPlate, but alas... I don't think there is.

Please add a ShadCN/UI option - or tell me how I can help in any way. I am familiar with building CLIs with Node.js, Python, Bun, Bash, and (sadly) even C++ and Powershell (ewww 🤮), so tell me what I can help with first!