Add documentation to use Nebius Token Factory on strands

[Arindam200]

Description

This PR adds comprehensive documentation for Nebius Token Factory as a community-maintained model provider. The documentation follows the same structure and patterns as the existing Fireworks AI provider documentation, providing users with clear instructions on how to integrate Nebius Token Factory models with the Strands Agents SDK using the OpenAI compatibility layer.

Fixes: #395

Type of Change

• New content addition

Motivation and Context

Nebius Token Factory is a fast inference service for open-source language models that provides OpenAI-compatible API access. Adding this documentation enables users to easily discover and integrate Nebius Token Factory models into their Strands Agents applications. This addition expands the available community model provider options and follows the established pattern for documenting OpenAI-compatible providers.

Areas Affected

• New file: docs/community/model-providers/nebius-token-factory.md - Main documentation page with installation, usage, configuration, troubleshooting, and references
• New file: docs/user-guide/concepts/model-providers/nebius-token-factory.md - Redirect file that routes users from the user guide to the community documentation
• Updated: mkdocs.yml - Added navigation entries in two locations:
  • User Guide > Concepts > Model Providers (with community superscript)
  • Community > Model Providers

Screenshots

Checklist

• I have read the CONTRIBUTING document
• My changes follow the project's documentation style
• I have tested the documentation locally using mkdocs serve
• Links in the documentation are valid and working
• Images/diagrams are properly sized and formatted
• All new and existing tests pass

Additional Notes

• Documentation follows the same structure as Fireworks AI provider documentation for consistency
• Uses OpenAI compatibility layer (same as Fireworks AI), requiring strands-agents[openai] dependency
• Includes example model IDs: deepseek-ai/DeepSeek-R1-0528 and meta-llama/Meta-Llama-3.1-70B-Instruct
• Base URL: https://api.tokenfactory.nebius.com/v1/
• All external links point to official Nebius Token Factory documentation

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.