* feat: enhance codex provider resolution with shortcut aliases and improved base URL handling
* fix: enhance codex alias resolution to include shell model
* feat: enhance Codex provider resolution to support new aliases and base URL handling
* fix: update base URL resolution logic for Codex models in GitHub mode
* fix: update provider transport logic to enforce Codex responses and adjust base URL handling
* fix: update provider request resolution to respect custom base URLs and adjust transport logic
* fix: restore OPENAI_MODEL environment variable handling in tests and provider config