feat(appstore): add AppStore client features

- AppStoreJsBridge: JS bridge for native APK install, version check, update
- InstalledAppDao, InstalledApp entity: Room DB for tracking installed apps
- UpdateCheckerWorker: background update polling via WorkManager
- InstallerService: APK download + SHA-256 verify + PackageInstaller session
- Updated AndroidManifest: REQUEST_INSTALL_PACKAGES, FileProvider, receivers
- Updated MainActivity: notification channel, WorkManager, JS bridge wiring
- config.json: targetUrl = https://store.silverlabs.uk
- file_paths.xml: FileProvider paths for APK installs

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

app/src/main/kotlin/uk/silverlabs/silverdroid/data/PwaDatabase.kt

@@ -4,15 +4,17 @@ import android.content.Context
 import androidx.room.Database
 import androidx.room.Room
 import androidx.room.RoomDatabase
+import uk.silverlabs.silverdroid.data.model.InstalledApp
 import uk.silverlabs.silverdroid.data.model.PwaApp
 
 @Database(
-    entities = [PwaApp::class],
-    version = 1,
+    entities = [PwaApp::class, InstalledApp::class],
+    version = 2,
     exportSchema = true
 )
 abstract class PwaDatabase : RoomDatabase() {
     abstract fun pwaAppDao(): PwaAppDao
+    abstract fun installedAppDao(): InstalledAppDao
 
     companion object {
         @Volatile