create the right config file on the first setup

[smallnest]

Version / branch / commit

zero dev

OS and environment

macOS 26.5.1/ Ghostty/Go1.27rc1

Steps to reproduce

1. git clone ....
2. go run cmd/zero or go run cmd/zero setup

Expected behavior

create the initial config.json and setup the first provider

Actual behavior

active provider "" not found

Relevant logs, screenshots, or error messages