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/tools/sample_will.json

@@ -0,0 +1,26 @@
+{
+  "imp-heiress-1": {
+    "tx": "0f1e2d3c4b5a69788796a5b4c3d2e1f0112233445566778899aabbccddeeff00",
+    "addr": "bc1qdeadbeef0",
+    "amount": 100000,
+    "tag": "heiress-1",
+    "metadata": {},
+    "notify": "heir1@example.invalid"
+  },
+  "imp-heiress-2": {
+    "tx": "112233445566778899aabbccddeeff00112233445566778899aabbccddeeff0011",
+    "addr": "bc1qdeadbeef1",
+    "amount": 200000,
+    "tag": "heiress-2",
+    "metadata": {},
+    "notify": "heir2@example.invalid"
+  },
+  "imp-heiress-3": {
+    "tx": "a1b2c3d4e5f60718293a4b5c6d7e8f901a2b3c4d5e6f708192a3b4c5d6e7f809",
+    "addr": "bc1qdeadbeef2",
+    "amount": 300000,
+    "tag": "heiress-3",
+    "metadata": {},
+    "notify": "heir3@example.invalid"
+  }
+}