feat(screenshots): Set up localized Play Store screenshot pipeline

- Add Compose screenshot test infrastructure (build config, screenshotTest source set)

- Add 7 localized screenshots covering all key app screens

- Device spec set to Pixel 8 (1080x2400, 428dpi); batch size 4 for 1080p memory budget

- Add screen title heading and fix appearance card header layout in WidgetConfigurationScreen

- Balance padding on requires-Pro notice in widget config bottom bar

settings.gradle

@@ -1,2 +1,10 @@
+pluginManagement {
+    repositories {
+        google()
+        mavenCentral()
+        gradlePluginPortal()
+    }
+}
+
 rootProject.name = "Companion App for AirPods"
 include ':app'