- completely redesign UI with improved layout and responsive design

- add dark mode support with transitions
- implement challenge sharing functionality using LZString compression
- add print feature for challenges
- improve history management with date formatting and load/delete options
- implement toasts for user notifications
- add modal for social sharing options (Twitter, Facebook, Reddit, Email)
- enhance form validation and user feedback
- optimize mobile experience with better spacing and controls
- replace basic alerts with modern toast notifications
- add random game suggestion feature
- implement custom challenge type toggle

Author: TobiasMue91