Notifikasi transaksi: hanya untuk admin + transaksi dari orang lain (bukan transaksi sendiri)

lib/main.dart

@@ -1,13 +1,16 @@
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 import 'package:provider/provider.dart';
 import 'package:supabase_flutter/supabase_flutter.dart';
 
 import 'config.dart';
+import 'models/sale.dart';
 import 'state/app_state.dart';
 import 'services/printer_service.dart';
 import 'screens/login_screen.dart';
 import 'screens/home_page.dart';
 import 'utils/colors.dart';
+import 'utils/format.dart';
 
 void main() async {
   WidgetsFlutterBinding.ensureInitialized();
@@ -25,12 +28,48 @@ class MyApp extends StatefulWidget {
 
 class _MyAppState extends State<MyApp> with WidgetsBindingObserver {
   late final AppState _appState;
+  final GlobalKey<ScaffoldMessengerState> _scaffoldKey =
+      GlobalKey<ScaffoldMessengerState>();
 
   @override
   void initState() {
     super.initState();
     _appState = AppState();
     WidgetsBinding.instance.addObserver(this);
+    // Dengarkan stream notifikasi transaksi baru (dari HP lain / checkout).
+    _appState.newSaleNotifications.stream.listen(_showSaleNotification);
+  }
+
+  void _showSaleNotification(Sale sale) {
+    final messenger = _scaffoldKey.currentState;
+    if (messenger == null) return;
+    // Getar + bunyi notifikasi.
+    HapticFeedback.heavyImpact();
+    SystemSound.play(SystemSoundType.click);
+    // Banner notifikasi di atas layar.
+    messenger.showSnackBar(
+      SnackBar(
+        content: Row(
+          children: [
+            const Icon(Icons.check_circle, color: kSuccess, size: 20),
+            const SizedBox(width: 10),
+            Expanded(
+              child: Text(
+                'Transaksi baru: ${sale.items.fold<int>(0, (s, i) => s + i.qty)} item • ${formatRupiah(sale.total)}',
+                style: const TextStyle(color: kText, fontWeight: FontWeight.w600),
+              ),
+            ),
+          ],
+        ),
+        backgroundColor: kSurface,
+        behavior: SnackBarBehavior.floating,
+        duration: const Duration(seconds: 4),
+        shape: RoundedRectangleBorder(
+          borderRadius: BorderRadius.circular(14),
+          side: const BorderSide(color: kSuccess, width: 1),
+        ),
+      ),
+    );
   }
 
   @override
@@ -54,6 +93,7 @@ class _MyAppState extends State<MyApp> with WidgetsBindingObserver {
     return ChangeNotifierProvider.value(
       value: _appState,
       child: MaterialApp(
+        scaffoldMessengerKey: _scaffoldKey,
         title: 'Dutra Store',
         debugShowCheckedModeBanner: false,
         theme: ThemeData(