- completely redesign image to ASCII art converter UI with modern layout

- add dark mode support with theme persistence in localStorage
- implement drag-and-drop file upload functionality
- add detail presets (low, medium, high) for quick configuration
- improve image processing with brightness, contrast and invert controls
- add multiple character set options including custom characters
- implement color mode options (none, original, grayscale)
- add font size controls for ASCII output display
- add copy and download functionality for generated ASCII art
- optimize rendering with `requestAnimationFrame` and debouncing
- implement responsive design for mobile compatibility
- add proper meta tags for SEO and social media sharing

Author: TobiasMue91