feat: add Qwen OAuth integration and provider support

- Add Qwen OAuth authentication support via /onboard-qwen command
- Implement Qwen provider configuration in provider manager UI
- Add Qwen-specific API client handling with proper headers and token refresh
- Include Qwen in model configuration and provider detection logic
- Add Qwen credentials management and storage at ~/.qwen/oauth_creds.json
- Support Qwen model (qwen3-coder-plus) with portal.qwen.ai endpoint

Co-authored-by: Claude Opus 4.6 <noreply@openclaude.dev>

Author: euxaristia

.gitignore

@@ -10,3 +10,4 @@ GEMINI.md
 package-lock.json
 /.claude
 coverage/
+.openclaude/settings.local.json