Delay iOS PR comment until the public simulator list is ready

[DjDeveloperr]

Summary

• Added a public readiness gate to the iOS comment session so the PR link is only posted after the tunnel can serve /api/simulators and the selected simulator appears booted.
• Added a regression test that locks the comment step behind the new readiness check.
• Updated the GitHub Actions guide to reflect the new iOS session behavior.

Testing

• npm run test:github-actions
• npm exec -- prettier --check actions/run-ios-comment-session/action.yml docs/guide/github-actions.md package.json scripts/github-actions.test.mjs
• git diff --check