feat(api): add audio-mini model choices (#3886)

## Summary

Adds typed model names for gpt-audio-mini and gpt-audio-mini-2025-12-15.

## Changes

- Add both audio-mini model names to shared and Responses model choices
- Preserve all existing accepted model names for compatibility

Co-authored-by: jbeckwith-oai <269036200+jbeckwith-oai@users.noreply.github.com>