Offline sync: indikator status sinkron di Riwayat + retry antrean otomatis

lib/state/app_state.dart

@@ -248,6 +248,15 @@ class AppState extends ChangeNotifier {
 
   final OfflineQueueService _offlineQueue = OfflineQueueService();
 
+  /// ID transaksi yang masih dalam antrean offline (belum terkirim ke server).
+  Set<String> get pendingSaleIds => _offlineQueue.pendingSaleIds;
+
+  /// True jika transaksi dengan [saleId] masih menunggu sinkronisasi.
+  bool isSalePending(String? saleId) => _offlineQueue.isPending(saleId);
+
+  /// Jumlah transaksi offline yang belum tersinkron (badge di Riwayat).
+  int get pendingOfflineCount => _offlineQueue.pendingSaleIds.length;
+
   double get subtotal =>
       cart.fold(0, (sum, line) => sum + line.price * line.qty);