Android 1.3.1 (versionCode 6)

Backdated release, created retroactively when the ios-v*/android-v* tagging convention was introduced. This repo's Android/ directory was merged in as squashed history with no per-version commits, so this tag points at the earliest available Android-touching commit rather than the true original release commit — the tag date does not reflect the actual original release date. The attached APK is the exact one already distributed via the self-hosted F-Droid repo for this version.