android: add BAL Reader app (Chaquopy codec bridge) + frame progress bar

First commit of the Android 'BAL Reader' app: a camera scanner that decodes
the same four transfer formats the plugin exports (BAL QR v2/legacy, BC-UR
v1/v2, BBQR) by running the synced bal/core codecs verbatim under Chaquopy
plus a verify_chain regression. Adds android/scripts/build_apk.py (resync
codecs, gradle build, prints APK sha256) and sync_codecs.py.

UI: during capture a thin mint fill-bar above the camera preview shows
received/total frames (FrameProgressBar), complementing the exact n/N label.

android/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,7 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.14-bin.zip
+networkTimeout=10000
+validateDistributionUrl=true
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists