Prepare reproducible F-Droid release

[andre487]

Summary

• add English and Russian Fastlane metadata and store graphics
• add an F-Droid source-build recipe pinned to the upstream signing certificate
• publish a signed universal APK for F-Droid reproducible-build verification
• bump the app to 0.0.4 and remove the generated sources JAR from Git

Verification

• native tests and release Android unit tests pass
• all five signed release APKs build successfully
• the universal APK contains all four supported ABIs
• two clean unsigned universal builds are byte-identical
• every signed APK is checked against the pinned SHA-256 certificate fingerprint