Flutter: Update Android Config for Release Build

[moven0831]

Background

Previously, our Android release builds were incompatible with code shrinking and obfuscation due to UniFFI's dependency on JNA. This resulted in runtime crashes:

E/AndroidRuntime(17363): java.lang.UnsatisfiedLinkError: Can't obtain peer field ID for class com.sun.jna.Pointer

• See related issue: https://github.com/privacy-ethereum/zkID/issues/40

Solution

With the migration to Flutter Rust Bridge (FRB) in #583, we've removed the UniFFI/JNA dependency. This enables us to re-enable Android build optimizations that were previously disabled as a workaround.

Tasks

• [ ] Enable code shrinking and obfuscation in android/app/build.gradle
  • Update minifyEnabled and shrinkResources flags
  • Configure ProGuard/R8 rules if needed
• [ ] Update documentation at https://zkmopro.org/docs/setup/flutter-setup#%EF%B8%8F-error-when-running-flutter-run---release
  • Remove workaround instructions for the UniFFI/JNA issue
  • Add guidance for the new FRB-based configuration

References

• Flutter Rust Bridge: https://github.com/fzyzcjy/flutter_rust_bridge
• Migration PR: #583