- completely redesign color picker UI with modern card-based layout

- add dark mode support with theme toggle and localStorage persistence
- implement color harmonies (complementary and analogous colors)
- add accessibility contrast checker with WCAG compliance indicators
- add color history feature that stores recently used colors
- implement RGB sliders for precise color adjustment
- add color name identification for common colors
- improve output format display with dedicated copy buttons
- add hex color input field for manual entry
- enhance responsive design for mobile compatibility

Author: TobiasMue91