TAPSIGNER backup test 7963102

Prerelease APKs for testing TAPSIGNER encrypted backup export from commit 7963102.\n\nChanges:\n- Offers Save encrypted backup after an initialized TAPSIGNER is detected/imported.\n- Lets the user choose an .aes backup file location with Android's document picker.\n- Verifies the Coinkite certificate/check path before authenticated backup.\n- Sends the Tap Protocol backup command and writes the returned encrypted data bytes directly to disk.\n- Re-reads and displays backup count after backup.\n\nUse the release APK for normal install testing. Debug APK is included for troubleshooting.