[FEATURE] Document Nebius Serverless Endpoints in the LLM guide

Feature Area

Documentation

Is your feature request related to a an existing bug? Please link it here.

N/A

Describe the solution you'd like

The LLM guide documents Nebius AI Studio / Token Factory, but users running their own model on a Nebius Serverless Endpoint need different configuration: the endpoint URL, its bearer token, and the exact served model ID.
I’ve prepared a documentation change using CrewAI’s existing custom_openai=True support. It adds:

• Endpoint configuration and authentication instructions.
• A small Agent/Task/Crew example with a local arithmetic tool.
• Model and vLLM tool-calling prerequisites.
• Readiness, streaming, troubleshooting and cleanup guidance.
• Matching English, Arabic, Korean and Brazilian Portuguese sections.
  The example links to the existing vLLM deployment guide for Nebius Serverless. No runtime changes or new dependencies are needed.

Describe alternatives you've considered

No response

Additional context

No response

Willingness to Contribute

Yes, I'd be happy to submit a pull request

Start with the LLM guide’s existing Nebius AI Studio / Token Factory documentation and the project’s custom_openai=True support. Use the linked vLLM deployment guide for Nebius Serverless as the external reference, then verify the English, Arabic, Korean, and Brazilian Portuguese sections cover configuration, authentication, prerequisites, readiness, streaming, troubleshooting, and cleanup.