PR Summary:

This PR adds the pyByggstyrning extension to the extensions.json file. The extension provides tools for model-based construction and includes all required metadata such as name, description, author information, repository URL, and website. The JSON structure remains valid with the addition of this new extension.

Review Summary:

I've reviewed the changes and found that the PR successfully adds the new extension to the extensions.json file with all required fields. The changes maintain the proper JSON structure and format. I found no issues that would prevent merging. Feel free to provide feedback on this review for future improvements.

Follow-up suggestions:

@devloai update the documentation to include the new extension if there's a list of available extensions somewhere in the docs.