- completely redesign image converter UI with modern interface

- implement drag and drop file upload functionality
- add file preview thumbnails with size information
- introduce additional image processing options:
  - resize with custom dimensions
  - rotate images (0°, 90°, 180°, 270°)
- improve conversion process with better progress indicators
- add results table showing size reduction statistics
- implement toast notifications for user feedback
- enhance mobile responsiveness with tailwind classes
- replace basic `JSZip` implementation with more robust solution
- optimize file validation (type checking, 10MB size limit)

Author: TobiasMue91