fix: let Android Keystore generate secret IVs

[faheemKamboh]

Summary

• fix shared-secret encryption on devices that reject caller-provided AES-GCM IVs with Android Keystore randomized encryption enabled
• let Android Keystore generate the AES-GCM IV and store that IV with the ciphertext
• bump Android metadata to versionCode 8 / versionName 0.1.7 for signed in-place update from v0.1.6
• document the compatibility note and release intent

Validation

• git diff --check
• permission scan confirms SEND_SMS only; no READ_SMS or camera permission
• local Android unit/build not run because Java is unavailable in this shell; GitHub Actions must validate unit tests and signed APK build

Task: QasidRelay v0.1.x field-test unblock