* Update documentation images
* Introduce native vertical EPUB reader for Desktop
* Add libsecret support for Linux secret storage
* Update localized strings and plurals across multiple languages
* Update PDF annotation UI and highlighter settings on desktop
This commit introduces a complete overhaul of the `README.md` to improve project presentation. Key changes include:
• Adds a new header with the app icon and a Google Play badge.
• Updates the feature graphic and includes a note distinguishing the OSS version from the Play Store version.
• Refines the "Open Source Libraries" section to be more structured.
• Moves the main preview image into the `docs` directory.
Additionally, the `app/build.gradle.kts` file is updated to configure a standardized naming convention for output APK files, including flavor, version, and build type.
