Probes http://127.0.0.1:11434/api/tags (the standard Ollama
endpoint) with a short HTTP HEAD-style GET. Returns TRUE
only if the request returns HTTP 200 in under timeout_s
seconds. Used by vlm_pick_provider for the
provider = "auto" fallback chain. Override the URL via
options(soilKey.ollama_url = "http://host:port").
