feat: merge existing tailwind config

[juliusmarminge]

this merges the existing tailwind config to not remove any existing config when initializing the shadcn-ui config.

before (custom font settings was removed):

after (font config is preserved):

note that it's json-quoted but i don't think this is an issue as the previous solution also didn't produce an output that adhered to the user's formatting rules (use of single-quotes, semis etc etc). could ship prettier and run that on the file before writing, but with other formatters like biome getting popular i don't think this is worth it, and a manual save by the user is adequate)

[vercel]

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

A member of the Team first needs to authorize it.

[Nsttt]

That's looks good to me