- Add /api/ai/test/{provider} endpoint for testing individual providers
- Add 'Test' button to each provider accordion (visible when configured)
- Shows test result inline (success/error message)
- Update help links with direct URLs to API key pages:
- Anthropic: console.anthropic.com/settings/keys
- OpenAI: platform.openai.com/api-keys
- DeepSeek: platform.deepseek.com/api_keys
- Ollama: ollama.ai