docs: redirect default ReadTheDocs root to stable version

[Amitjoiya]

Summary

This PR updates the ReadTheDocs configuration so that the default
documentation (https://sbi.readthedocs.io/en/) redirects to the stable
version rather than latest, as requested in issue #1708.

Changes

• Added a redirects rule to .readthedocs.yml to point / → /en/stable/.

No other files were modified.

[janfb]

Thanks for addressing this @Amitjoiya !

The redirect is certainly one solution. but could you please check whether there is a setting in the Readthedocs settings to just have the stable version as the default site?

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Additional details and impacted files

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[Amitjoiya]

Hi @janfb ,
I checked the ReadTheDocs dashboard on my fork, but it only shows latest in the “Default version” dropdown — the stable version isn’t available there.
This makes sense because RTD only builds stable for the main project, not for forks.

So the “Default version → stable” change can only be applied on the official SBI ReadTheDocs project, where the stable build exists.

My PR adds the redirect as a fallback, but the actual fix requires switching:
RTD Project → Advanced Settings → Default version → stable
on the main project.

Happy to update/remove the redirect depending on what you prefer.

[janfb]

yes, that's much better, please go ahead with this solution.

[Amitjoiya]

@janfb , Good morning!
Thanks for the clarification. I’ve updated the .readthedocs.yaml file exactly as advised and ensured there are no formatting or whitespace issues left.
Pre-commit is clean now and the redirect is working correctly for / → /en/stable/.

If there’s anything else that needs refinement, I’d be happy to adjust it.
Thanks again for guiding me — learning a lot from this!

[janfb]

Thanks for the changes and looking further into this.

It seems we were too slow here and there was a settings-based solution that @michaeldeistler found and applied just now.

Sorry about that, @Amitjoiya - Your initiative here is nevertheless much appreciated!

You are welcome to have a look at another issue. Please comment below the issue you are interested in to first discuss how to solve it, before opening a PR - Thank you!