Handle failures of init_model_providers() gracefully #161

Minor: If init_model_providers() fails (e.g., network issue, API down during startup), the application might not start gracefully or might hit RuntimeErrors later. In the future, we probably want to think how critical failures during init_model_providers should be handled at the application entry points (api.py, app.py).

Originally posted by @EmilienM in #154 (comment)