fix(android): keep system back working on Android 16 (targetSdk 36)

On Android 16 / targetSdk 36, android:enableOnBackInvokedCallback defaults
to true, so the OS routes the back gesture and the 3-button back through
OnBackInvokedDispatcher instead of dispatching KEYCODE_BACK. Qt does not
register an OnBackInvokedCallback, so the platform's default callback
finishes the activity and the app closes from any sub-screen, instead of
navigating back via MobileApplication.qml's Keys.onBackPressed -> backAction().

Opt out of the predictive back callback to restore legacy KEYCODE_BACK
delivery. Verified on a Pixel 8a (Android 16): edge-swipe and 3-button back
now return to the previous screen; double-back-to-exit on the main screen
still works.

Fixes #152

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: 1technophile

assets/android/AndroidManifest.xml

@@ -59,7 +59,8 @@
                  android:label="Theengs BLE"
                  android:allowBackup="true"
                  android:fullBackupContent="@xml/backup_rules"
-                 android:dataExtractionRules="@xml/data_extraction_rules">
+                 android:dataExtractionRules="@xml/data_extraction_rules"
+                 android:enableOnBackInvokedCallback="false">
 
         <!-- Activity -->
         <activity android:name="org.qtproject.qt.android.bindings.QtActivity"