docs: Integration with Nebius AI Studio

[Aktsvigun]

Thank you for contributing to LangChain!

[x] PR title: langchain_ollama: support custom headers for Ollama partner APIs

Where "package" is whichever of langchain, core, etc. is being modified. Use "docs: ..." for purely docs changes, "infra: ..." for CI changes.
Example: "core: add foobar LLM"
[x] PR message:

**Description: This PR adds support for passing custom HTTP headers to Ollama models when used as a LangChain integration. This is especially useful for enterprise users or partners who need to send authentication tokens, API keys, or custom tracking headers when querying secured Ollama servers.
Issue: N/A (new enhancement)
**Dependencies: No external dependencies introduced.
Twitter handle: @arunkumar_offl
[x] Add tests and docs: If you're adding a new integration, please include
1.Added a unit test in test_chat_models.py to validate headers are passed correctly.
2. Added an example notebook: docs/docs/integrations/llms/ollama_custom_headers.ipynb showing how to use custom headers.

[x] Lint and test: Ran make format, make lint, and make test to ensure the code is clean and passing all checks.

Additional guidelines:

Make sure optional dependencies are imported within a function.
Please do not add dependencies to pyproject.toml files (even optional ones) unless they are required for unit tests.
Most PRs should not touch more than one package.
Changes should be backwards compatible.
If no one reviews your PR within a few days, please @-mention one of baskaryan, eyurtsev, ccurme, vbarda, hwchase17.

This MR is only for the docs. Added integration with Nebius AI Studio to docs. The integration package is available at https://github.com/nebius/langchain-nebius.

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Name	Status	Preview	Comments	Updated (UTC)
langchain	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Jun 14, 2025 8:10pm

[Aktsvigun]

@ccurme Hello! Kindly approve :) This PR is only for the documents, all the checks have been successfully passed.

[Aktsvigun]

Hi @baskaryan @eyurtsev @vbarda @hwchase17 ! Could you please review this docs-only MR? Some checks already started failing after I updated with current master state, even though they were passing successfully previously.

[codspeed-hq]

CodSpeed Walltime Performance Report

Merging #31293 will not alter performance

_{Comparing Aktsvigun:master (ff9ecac) with master (01fcdff)}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

✅ 13 untouched benchmarks

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #31293 will not alter performance

_{Comparing Aktsvigun:master (ff9ecac) with master (01fcdff)}

Summary

✅ 13 untouched benchmarks