i18n: add Swedish (sv) locale

I would like to add Swedish (`sv`) as a supported ComfyUI interface language and help maintain/review the translations.

I checked the current locale structure and the translation contribution guide. Swedish is not currently listed among the supported locales, and there is no existing request for it. I can follow the documented process: add the locale configuration and let the project’s release workflow generate the initial four locale files, then perform native-speaker review.

Could a maintainer confirm that `sv` is the preferred locale code and advise whether there are any Swedish-specific terminology guidelines to follow?

Start with the translation contribution guide and the existing locale configuration, then compare how another supported locale is registered. Confirm that `sv` is the preferred code and check for Swedish terminology guidance before using the release workflow to generate the four locale files. Done means Swedish is listed as a supported interface language and the generated translations have received native-speaker review.

Written by the indexing model from the issue text.