feat(android): foreground service for real-time notification polling

- New NotificationForegroundService: persistent foreground coroutine-based
  polling every 30s, keeps app alive in background
- Manifest: FOREGROUND_SERVICE + FOREGROUND_SERVICE_DATA_SYNC permissions,
  service declaration with foregroundServiceType=dataSync
- NotificationHelper: added silent channel for persistent service notification
- ServerManagerApp: starts foreground service on app launch
- MainActivity: removed redundant NotificationWorker.checkNow (service handles
  background polling; NotificationPoller still handles in-app refresh)
- Bump to v1.8.0 (versionCode 12)

android/app/src/main/AndroidManifest.xml

@@ -6,6 +6,8 @@
     <uses-permission android:name="android.permission.REQUEST_INSTALL_PACKAGES" />
     <uses-permission android:name="android.permission.DOWNLOAD_WITHOUT_NOTIFICATION" />
     <uses-permission android:name="android.permission.POST_NOTIFICATIONS" />
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE_DATA_SYNC" />
     <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
 
     <application
@@ -35,6 +37,11 @@
             </intent-filter>
         </receiver>
 
+        <service
+            android:name=".service.NotificationForegroundService"
+            android:foregroundServiceType="dataSync"
+            android:exported="false" />
+
         <provider
             android:name="androidx.core.content.FileProvider"
             android:authorities="${applicationId}.fileprovider"