text: Title: docs: toggle Gurubase widget theme with original documentation one
  Body: ![Image](https://github.com/user-attachments/assets/c6e7dcb4-f543-4f5b-bdc8-c2d54d56fb2c)
  
  We should switch Gurubase widget theme accordingly to documentation preffered one. Gurubase has already written example how it should be implemented with mkdocs
  
  https://github.com/Gurubase/gurubase-widget/issues/17
  https://github.com/Gurubase/gurubase-widget/blob/master/examples/mkdocs/docs/js/theme-switch.js