Adds ndk.abiFilters = ["arm64-v8a"] to the release build type only, so
the release APK/AAB ship a single ABI instead of a universal build with
armeabi-v7a, x86, and x86_64. defaultConfig and the debug type are left
untouched: CI's E2E matrix runs the debug build on x86_64 emulators and
needs the x86_64 native libs (incl. libsqlcipher.so).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>