- completely redesign word counter UI with modern card-based layout

- add dark/light theme toggle with localStorage persistence
- implement tabbed interface for basic stats, advanced stats, and word frequency
- add new metrics: reading time, sentences, paragraphs, readability score
- add text actions: copy to clipboard and download functionality
- improve responsive design with mobile-friendly layout
- enhance text analysis with word frequency table
- implement tooltips for metric explanations
- optimize CSS with CSS variables and responsive breakpoints
- replace sidebar.js with logo.js

Author: TobiasMue91