[codex] Add OpenAI CLI skill

[jxnl-oai]

Summary

• add the openai-cli curated skill to the public skills catalog
• keep the same focused skill structure already reviewed internally: Responses, structured extraction, files/tools, images, speech, transcription, and Admin API workflows
• make the public repo installable via npx skills add openai/skills --skill openai-cli

Validation

• npx skills add /Users/jasonliu/dev/openai-skills --skill openai-cli --list