- Add Txt library for loading and parsing plain text files
- Create TxtReaderActivity with streaming page rendering
- Uses 8KB chunks to handle large files without memory issues
- Page index caching for fast re-open after sleep
- Progress bar during initial indexing
- Word wrapping with UTF-8 support
- Support cover images for TXT files
- Priority: same filename as TXT (e.g., book.jpg for book.txt)
- Fallback: cover.bmp/jpg/jpeg in same folder
- Converts JPG to BMP using existing converter
- Update SleepActivity to show TXT cover images in Cover mode
- Add .txt extension to file browser filter
