feat(appstore): rebrand as SilverSHELL AppStore client

- applicationId: uk.silverlabs.silverdroid → uk.silverlabs.appstore
- app_name: SilverDROID → SilverSHELL AppStore
- user agent: SilverDROID/1.0 → SilverAppStore/1.0
- versionCode/versionName: override via Gradle -P args for CI builds

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/build.gradle.kts

@@ -11,11 +11,11 @@ android {
     compileSdk = 35
 
     defaultConfig {
-        applicationId = "uk.silverlabs.silverdroid"
+        applicationId = "uk.silverlabs.appstore"
         minSdk = 26
         targetSdk = 35
-        versionCode = 1
-        versionName = "1.0.0"
+        versionCode = (project.findProperty("versionCode") as String?)?.toInt() ?: 1
+        versionName = (project.findProperty("versionName") as String?) ?: "1.0.0"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
         vectorDrawables {
@@ -84,6 +84,9 @@ dependencies {
     implementation("androidx.room:room-ktx:2.6.1")
     ksp("androidx.room:room-compiler:2.6.1")
 
+    // WorkManager for background update checks
+    implementation("androidx.work:work-runtime-ktx:2.10.0")
+
     // Coroutines
     implementation("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.10.1")