Update bundled OpenAI Docs skill freshness check

[kkahadze-oai]

Summary

Sync the bundled openai-docs system skill with the already-merged openai/skills update from openai/skills#360.

Codex bundles system skills from codex-rs/skills/src/assets/samples, so this PR copies the same GPT-5.4 OpenAI Docs skill update into the Codex app/CLI bundle path.

Changes

• Add the latest-model resolver script to the bundled openai-docs skill.
• Route model upgrade and prompt-upgrade requests through remote latest-model metadata when current guidance is needed.
• Rename bundled fallback references to upgrade-guide.md and prompting-guide.md.
• Keep the bundled fallback guidance GPT-5.4-only.

Validation

• Verified this bundled skill is byte-for-byte identical to openai/skills@origin/main skills/.system/openai-docs.
• Ran the resolver locally and confirmed it returns gpt-5.4 / gpt-5p4.

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[kkahadze-oai]

I have read the CLA Document and I hereby sign the CLA

[kkahadze-oai]

recheck