Check provider connectivity

Remote providers call models.retrieve(model) (zero generation tokens); Ollama checks the model is present in /api/tags. The same check runs at save time and as the describe pre-flight.

Responses

{
  "provider_name": "ollama",
  "model": "qwen2.5-coder:latest",
  "is_local": true,
  "status": "healthy",
  "message": "model present"
}