* Implemented a custom theme engine for the EPUB reader, allowing users to switch between built-in themes (System, Light, Dark, Sepia, Slate, and OLED).
Key changes include:
- Added `ReaderThemePanel` and theme selection logic to `EpubReaderScreen`.
- Introduced a theme persistence layer using SharedPreferences.
- Updated `ChapterWebView` and `epub_reader.js` to dynamically apply background and text colors via JavaScript, including improved contrast adjustment for inline styles.
- Enhanced `CssParser` and `ContentStyler` in the paginated reader to adapt CSS colors based on the active theme's background and text luminance.
- Integrated theme-specific background and text colors into `PaginatedReaderScreen` and its layout components.
- Added a theme palette icon to the reader controls.
* Added custom theme builder and texture support to EPUB reader
* Refactored color picker(PDF) into shared components and enhanced EPUB theme editor
* Updated theme customization UI and improved WebView theme application efficiency
* Updated page flip animation to use paper color with a theme-based tint
* Improved state restoration during paginated reader reconfiguration
