use FCM-matching tag so local notif replaces Google's bare push

lib/services/notification/notification_service.dart

@@ -259,6 +259,12 @@ class NotificationService {
     //   - otherwise → MessagingStyle (compact)
     final useBigPicture = notifType.contains('1') || bigPicturePath != null;
 
+    // Use the same tag the backend put on the FCM notification so this
+    // local notification REPLACES the bare one Android already drew when
+    // the push arrived — no duplicate, just the cover image.
+    final notifTag =
+        (data.id != null && data.id!.isNotEmpty) ? 'didvan-content-${data.id}' : null;
+
     final AndroidNotificationDetails androidPlatformChannelSpecifics =
         AndroidNotificationDetails(
       'content',
@@ -267,6 +273,7 @@ class NotificationService {
       importance: Importance.max,
       priority: Priority.high,
       playSound: true,
+      tag: notifTag,
       styleInformation: useBigPicture && bigPicturePath != null
           ? BigPictureStyleInformation(
               FilePathAndroidBitmap(bigPicturePath),