Updated Codex GitHub auth guidance

Property	Value
description	Recorded the GitHub PAT environment variable fallback for Codex shell sessions.
version	0.5.4
type	Update
related	MAC, MAC CLI

• Recorded GITHUB_PAT_TOKEN as the Windows user environment variable for the GitHub PAT used by Codex shell sessions.
• Documented mapping GITHUB_PAT_TOKEN to GH_TOKEN when gh CLI auth is stale inside Codex.
• Kept token handling environment-only: do not print the PAT, write it into repo files, or store it in Git remotes.