feat: add history sync worker

app/src/main/java/com/bitcointxoko/gudariwallet/util/NotificationHelper.kt

@@ -45,6 +45,18 @@ object NotificationHelper {
                 setSound(null, null)
             }
         )
+
+        nm.createNotificationChannel(
+            NotificationChannel(
+                NotificationConstants.CHANNEL_SYNC,
+                context.getString(R.string.notif_channel_sync_name),
+                NotificationManager.IMPORTANCE_DEFAULT
+            ).apply {
+                description = context.getString(R.string.notif_channel_sync_desc)
+                enableVibration(false)
+                setSound(null, null)
+            }
+        )
     }
 
     // ── User-facing notifications ─────────────────────────────────────────────
@@ -92,6 +104,26 @@ object NotificationHelper {
         )
     }
 
+    /**
+     * Posts a notification when the one-time historical payment sync completes.
+     * No tap destination needed — the user is already in the app or will land
+     * on the main screen via the default MainActivity launch.
+     */
+    fun notifySyncComplete(context: Context, paymentCount: Int) {
+        val title = context.getString(R.string.notif_sync_complete_title)
+        val text  = context.getString(R.string.notif_sync_complete_text, paymentCount)
+        notify(
+            context,
+            NotificationConstants.NOTIF_ID_SYNC_COMPLETE,
+            NotificationCompat.Builder(context, NotificationConstants.CHANNEL_SYNC)
+                .setSmallIcon(R.drawable.ic_notification)
+                .setContentTitle(title)
+                .setContentText(text)
+                .setAutoCancel(true)
+                .build()
+        )
+    }
+
     // ── Foreground service notification ───────────────────────────────────────
 
     fun buildServiceNotification(context: Context): Notification {