Default language setting at user level

Description: Allow each user to set their preferred default language for creating new Knowbys. Currently new Knowbys default to English regardless of the user's location or preference.

Proposed behaviour: A language preference option in the user's profile/settings that sets the default language applied whenever they create a new Knowby. This would not affect other users in the organisation.

Use case: Organisations with multilingual teams — for example a Czech-speaking team within a global organisation — need their creators to be able to work in their own language by default without having to manually change the language each time.