49f97b69ca
## Summary * **What is the goal of this PR?** Add support for reading plain text (.txt) files, enabling users to browse, read, and track progress in TXT documents alongside existing EPUB and XTC formats. * **What changes are included?** - New Txt library for loading and parsing plain text files - New TxtReaderActivity with streaming page rendering using 8KB chunks to handle large files without memory issues on ESP32-C3 - Page index caching system (index.bin) for instant re-open after sleep or app restart - Progress bar UI during initial file indexing (matching EPUB style) - Word wrapping with proper UTF-8 support - Cover image support for TXT files: - Primary: image with same filename as TXT (e.g., book.jpg for book.txt) - Fallback: cover.bmp/jpg/jpeg in the same folder - JPG to BMP conversion using existing converter - Sleep screen cover mode now works with TXT files - File browser now shows .txt files ## Additional Context * Add any other information that might be helpful for the reviewer * Memory constraints: The streaming approach was necessary because ESP32-C3 only has 320KB RAM. A 700KB TXT file cannot be loaded entirely into memory, so we read 8KB chunks and build a page offset index instead. * Cache invalidation: The page index cache automatically invalidates when file size, viewport width, or lines per page changes (e.g., font size or orientation change). * Performance: First open requires indexing (with progress bar), subsequent opens load from cache instantly. * Cover image format: PNG is detected but not supported for conversion (no PNG decoder available). Only BMP and JPG/JPEG work.
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