* Add endpoint to resolve frontend user by auth method and username
* Require client ID for frontend user lookup
* Remove unnecessary if check
* Fix PromptRepository -> UserRepository
* Convert to protocol User
* Move User prep
* Address review comments
* 404 -> HTTP_404_NOT_FOUND
* Extract classes UserRepository and TaskRepository from PromptRepository
* move close_task() to TaskRepository and get_user_leaderboard to UserRepository()
* Use UserRepository in leaderboards endpoint, add type annotation to leaderboards endpoint