Fix deprecated build configuration warning

[callebtc]

Description:
The build generates a deprecation warning:

WARNING: The option setting 'android.defaults.buildfeatures.buildconfig=true' is deprecated.
The current default is 'false'.
It will be removed in version 10.0 of the Android Gradle plugin.

Impact:
Build will fail in future Android Gradle Plugin versions.

Fix Instructions:
Add the following to app/build.gradle.kts in the android block:

android {
    // ... existing config ...
    
    buildFeatures {
        buildConfig = true
    }
}

Alternative:
If BuildConfig is not needed, remove the deprecated setting and update code that references BuildConfig.

Files to Modify:

• app/build.gradle.kts

Priority: Medium - will become critical in future AGP versions