feat: add remote products and qr code for payconic

lib/models/remote_command.dart

@@ -170,6 +170,9 @@ class ServerProduct {
   /// Deleted on the website: hidden, kept for open tabs and the history.
   final bool archived;
 
+  /// The picture, at `/images/<imageId>`; null: none.
+  final String? imageId;
+
   const ServerProduct({
     required this.id,
     required this.name,
@@ -177,6 +180,7 @@ class ServerProduct {
     required this.priceInCents,
     this.lowStockThreshold,
     this.archived = false,
+    this.imageId,
   });
 
   factory ServerProduct.fromJson(Map<String, dynamic> json) {
@@ -187,6 +191,7 @@ class ServerProduct {
       priceInCents: json['priceInCents'] as int,
       lowStockThreshold: json['lowStockThreshold'] as int?,
       archived: json['archived'] as bool? ?? false,
+      imageId: json['imageId'] as String?,
     );
   }
 }