- completely redesign json formatter UI with modern styling

- add dark/light theme toggle with local storage persistence
- implement new features:
  - minify option
  - download functionality
  - file upload support
  - sample json data
  - expand/collapse all nodes
- improve JSON visualization with better syntax highlighting
- add keyboard shortcuts (ctrl+enter, esc, ctrl+c)
- add settings panel with indentation and sorting options
- implement notifications system for user feedback
- enhance error handling and validation
- optimize for mobile responsiveness

Author: TobiasMue91