Docs: runtime images and conda channel hosting (OH_CONDA_CHANNEL_ALIAS)

[enyst]

Summary

Adds a runtime guide explaining why conda-forge requests default to anaconda.org and how to avoid it when building your own runtime images by setting:

export OH_CONDA_CHANNEL_ALIAS=https://repo.prefix.dev

Related PR

• Implements the feature in OpenHands core: Configurable conda/mamba channel_alias for runtime builds + unit test OpenHands#11516

Details

• New page: openhands/runtime/runtime-images-and-conda.mdx
  • Two usage paths: prebuilt runtime images vs building yourself
  • Explains default channel_alias behavior and the new environment variable
  • Provides example alias values (public mirror or internal proxy)

Why

• Many organizations must avoid any contact with anaconda.org. Even when using only conda-forge, the default channel_alias expands to https://conda.anaconda.org/conda-forge.
• With the new knob, users can redirect conda-forge to a different host (e.g. https://repo.prefix.dev or an internal mirror).

Checklist

• New page linked under openhands/runtime/
• Language is concise and actionable

Co-authored-by: openhands [email protected]

@enyst can click here to continue refining the PR