Changes

PR #2056 by mikaelpr and ksylvan: feat: add Codex vendor with OpenAI OAuth

• Add new Codex AI vendor plugin with OpenAI OAuth PKCE flow
• Implement browser-based login with automatic token refresh on 401
• Allow explicit Codex model selection bypassing model listing
• Expose shared OpenAI BuildResponseParams and ExtractText helpers, and move system/developer messages into Codex instructions field
• Add comprehensive unit tests for Codex OAuth, streaming, and retry
• New internationalization keys added for all 11 languages.