Why

The ARC quickstart currently instructs readers to generate a legacy personal access token (classic) as the default way to authenticate ARC to GitHub. For repository and organization runners, GitHub recommends authenticating with a GitHub App instead; a personal access token (classic) is only required for runners at the enterprise level.

What changed

• The authentication step in the quickstart now points readers to the existing authentication guidance and recommends a GitHub App for repository and organization runners, while noting that a personal access token (classic) is required for enterprise-level runners.
• Added a note near the PAT-based example clarifying that readers using a GitHub App should configure \githubConfigSecret\ with the app credentials (\github_app_id, \github_app_installation_id, and \github_app_private_key) instead of \github_token.

Verification

• Anchor references in the updated links match existing section headings in the authentication guide.
• No content was removed from the PAT-based example, which remains valid (and required) for enterprise-level configurations.

Closes #37288