chore(scaffold): fix variant-specific test + redundant manifest label

Validated the scaffold with a real local build (Android SDK via Android
Studio: platform 35 + build-tools 35.0.0); `./gradlew lint test assembleDebug`
now passes end-to-end and produces a debug APK. Two fixes it surfaced:

- ScaffoldSanityTest asserted BuildConfig.DEBUG, which fails under
  testReleaseUnitTest (the `test` task runs both variants). Replace with a
  variant-agnostic VERSION_NAME check.
- Remove the redundant android:label on MainActivity (inherits the application
  label) — clears the RedundantLabel lint warning.

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

app/src/main/AndroidManifest.xml

@@ -20,7 +20,6 @@
         <activity
             android:name=".MainActivity"
             android:exported="true"
-            android:label="@string/app_name"
             android:theme="@style/Theme.RunicGateway">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />