This PR removes references to oai_gh from the curated GitHub skills and
replaces them with standard GitHub CLI auth guidance (gh auth login).
The goal is to avoid assuming internal tooling in a public repo.
That said, I'm not sure whether oai_gh is actually a built-in Codex
helper. If it is, feel free to close this PR.
I also did a sweep of .curated for other internal-only helpers and
didn't find any additional ones.