0.0.5

feat: add OpenAI Codex OAuth sign-in support

Add clanker auth login/logout/status commands for OpenAI OAuth.

- PKCE OAuth flow with auth.openai.com using Codex public client ID
- Token storage at ~/.clanker/openai-auth.json with auto-refresh
- Codex Responses API client with streaming support
- CLI ask/askWithHistory routes through Codex when OAuth is active
- Required state parameter for OAuth authorize request