- upgrade to bootstrap 5.3 with dark mode support

- add responsive layout with mobile-specific code view
- implement range sliders with live value indicators
- add new `gap` property support
- create preset system with local storage
- add ability to copy HTML code
- improve preview container with resize functionality
- add tooltips for flexbox properties
- enhance code generation with conditional output
- implement toast notifications for clipboard actions

Author: TobiasMue91