Fix auto-README workflow: land gpt-5-mini model update on main

[Copilot]

PR #46 updated the model in generate_readme.py from openai/gpt-4o to openai/gpt-5-mini, but merged into claude/github-ai-readme-action-beNGA instead of main. Since auto_readme.yml only triggers on main, the workflow kept using openai/gpt-4o and failing with HTTP 403 no_access.

• Root cause: merge target mismatch — fix never reached the branch the workflow runs on
• Fix: brings the model change to main

payload = {
    "model": "openai/gpt-5-mini",  # was openai/gpt-4o on main
    ...
}

Original prompt

See comments on Pull Request: #46

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