fix(openai_responses): add missing nano and mini models

[chrisgrieser]

Description

Add missing models gpt-5-mini and gpt-5-nano to the openai_reponses adapter. They are already present at the openai (completion) adapter.

Note for the PR review bot: the list is not alphabetical, I inserted the models based on their publication chronology.

Checklist

• I've read the contributing guidelines and have adhered to them in this PR
• I've added test coverage for this fix/feature → does not apply for just adding models
• I've run make all to ensure docs are generated, tests pass and my formatting is applied
• (optional) I've updated CodeCompanion.has in the init.lua file for my new feature → too small a change for this to be relevant.
• (optional) I've updated the README and/or relevant docs pages → too small a change for this to be relevant.

[olimorris]

Thanks for the PR. I intend for the responses adapter to be for models that support the v1/responses only.

[chrisgrieser]

May I ask why? considering that the completions API is deprecated by OpenAI, it should be preferred to use the responses API for any model that supports it.