- complete redesign of regex tester with modern UI and responsive layout

- add dark/light theme support with persistent preferences
- implement categorized regex examples with expandable sections
- add detailed match information with capture group highlighting
- add pattern explanation feature for regex understanding
- implement keyboard shortcuts (ctrl+enter, ctrl+g, etc.) for power users
- add safety timeouts to prevent browser freeze on complex patterns
- improve accessibility with proper ARIA attributes and focus states
- add toast notifications for user feedback
- replace basic styling with CSS variables for better theme support

Author: TobiasMue91