Can't `nuxflare init` with `yarn`

[brtinney]

This line assumes the command to install a package is {packageManager} install vs. {packageManager} add:

https://github.com/nuxflare/cli/blob/40c56d8703adc00fa6cf0ab7e84848744554d28d/src/commands/init.ts#L230C11-L230C81

This causes a fatal error when yarn is used.