The /model interactive picker resolved a base_url from user credentials
but never passed it to ProviderProfile.fetch_models(), causing the
picker to always query the provider's hardcoded default endpoint
instead of the user's custom URL (e.g. a company litellm proxy).
- providers/base.py: add optional base_url parameter to fetch_models()
- hermes_cli/models.py: pass resolved base_url to fetch_models()
- Update all subclass overrides for signature compatibility
- Add 6 regression tests covering override, fallback, and integration
