provider_model_ids() and list_authenticated_providers() had no case for
"ollama-cloud", so the /model slash command showed 0 models despite
fetch_ollama_cloud_models() being fully implemented. The CLI subcommand
worked because it called fetch_ollama_cloud_models() directly.
- Add ollama-cloud case to provider_model_ids() in models.py
- Populate curated dict for ollama-cloud in list_authenticated_providers()
- Add tests for both code paths