[ENH] npm package

[b-jonathan]

Description:
Let users run npx create-taco-app my-app instead of installing the Go binary manually.

How it works:
The npm package downloads the prebuilt Go binary on install and forwards commands to it.

Steps:

1. Create npm package structure under packages/create-taco-app/
2. Write postinstall.js — downloads the correct binary from GitHub Releases based on user's OS/arch
3. Write create-taco-app.js — runs taco init with forwarded args
4. Add GitHub Actions workflow to cross-compile Go binaries and upload as release assets on tagged
   releases
5. Publish create-taco-app to npm