Adds support for using ChatGPT Plus/Pro subscription-based authentication
in the CLI via OpenAI Codex OAuth, matching the existing VSCode extension
capability.
Changes:
- Add openai-codex as a supported CLI provider
- Add roo auth login-openai / logout-openai / status-openai commands
- Implement PKCE OAuth flow for CLI (reuses OpenAI auth endpoints)
- Store credentials in vscode-shim secret storage for transparent
integration with the existing OpenAiCodexHandler
- Update run.ts to validate OAuth credentials for openai-codex provider
- Add provider settings handling for openai-codex
- Add comprehensive tests for credential storage
Closes#11926
