feat: New Open Tab dialog with search and optional customer email. Drinks are now grouped per order. Payments trigger cha-ching and money rain.

lib/models/server_tab.dart

@@ -8,7 +8,15 @@ class ServerUnit {
   final DateTime addedAt;
   final DateTime? removedAt;
 
-  const ServerUnit({required this.id, required this.addedAt, this.removedAt});
+  /// The order it was rung up in; null for drinks from older app versions.
+  final String? orderId;
+
+  const ServerUnit({
+    required this.id,
+    required this.addedAt,
+    this.removedAt,
+    this.orderId,
+  });
 
   factory ServerUnit.fromJson(Map<String, dynamic> json) {
     return ServerUnit(
@@ -18,6 +26,7 @@ class ServerUnit {
         final String value => DateTime.parse(value).toLocal(),
         _ => null,
       },
+      orderId: json['orderId'] as String?,
     );
   }
 }
@@ -58,6 +67,7 @@ class ServerTabLine {
 class ServerTab {
   final String id;
   final String customerName;
+  final String? email;
   final DateTime openedAt;
   final int version;
   final List<ServerTabLine> lines;
@@ -65,6 +75,7 @@ class ServerTab {
   const ServerTab({
     required this.id,
     required this.customerName,
+    this.email,
     required this.openedAt,
     required this.version,
     this.lines = const [],
@@ -74,6 +85,7 @@ class ServerTab {
     return ServerTab(
       id: json['id'] as String,
       customerName: json['customerName'] as String,
+      email: json['email'] as String?,
       openedAt: DateTime.parse(json['openedAt'] as String).toLocal(),
       version: json['version'] as int? ?? 0,
       lines: [