Align with Nebius using the new default API endpoint

The default Nebius model endpoint is now api.tokenfactory.nebius.com. This aligns with Nebius updated platform and helps avoid legacy endpoints that may degrade or deprecate.

Details

• Default endpoint updated for new deployments
• If you still use AI Studio, set base_url explicitly to maintain continuity

Who this is for: Teams using Nebius-hosted models across environments.