feat(childPreferences): implement child preferences management

• Added childPreferencesEndpoints for managing child settings, including forbidden words and time restrictions.
• Created ChildPreferencesStore to handle preferences state, including fetching, updating, and saving preferences.
• Integrated preferences loading and saving in ChildPreferencesScreen, with error handling and loading states.

This enhances the user experience by allowing dynamic management of child preferences.

Closes IA-711