apply_llm_provider_args now resets llm_endpoint to Ollama's local
default when switching to a non-Anthropic provider without an explicit
endpoint and the stored endpoint is still Anthropic's fixed hosted
URL. Prevents a future per-use provider switch (SummaryPanel) that
only sends `provider` from silently leaving llm_endpoint pointed at a
third party for a provider that has no business talking to it.