[feat]: Expose framework stack to registry endpoint

[jguddas]

Feature description

Current User-Agent: shadcn
Suggested: User-Agent: shadcn/1.x.x (next-js; typescript; tailwind-v4)

This will allow registry providers to handle importing the right stuff, i.e. use the right Link component for each framework.

But I'm coming here with a solution, the actual problem is me doing import from "react" even when we don't use React.

Affected component/components

No response

Additional Context

ui/packages/shadcn/src/registry/fetcher.ts

Lines 48 to 51 in d28738b

	const requestHeaders = new Headers({
	Accept: "application/vnd.shadcn.v1+json, application/json;q=0.9",
	"User-Agent": "shadcn",
	})

Before submitting

• I've made research efforts and searched the documentation
• I've searched for existing issues and PRs