feat(app): implement Product Scan review flow, dynamic batch expiry picker, custom PDFs, PO relationships, and aligned card layouts

lib/features/camera/scan_mode_provider.dart

@@ -0,0 +1,3 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+final scanModeProvider = StateProvider<String>((ref) => 'DO');