Final commit.

lib/domain/entity/customer.dart

@@ -0,0 +1,53 @@
+import 'address.dart';
+
+/// Kunden-Stammdatensatz. Ein Kunde kann mehrere `CustomerContact`s haben
+/// (Ehepartner, Hausverwalter, …); diese werden separat in der
+/// `TourDetails.contacts`-Map geführt.
+class Customer {
+  const Customer({
+    required this.id,
+    required this.name,
+    required this.erpCustomerId,
+    required this.address,
+  });
+
+  final String id;
+  final String name;
+
+  /// ERP-Kundennummer (Legacy). Wird in der App nur informativ in der
+  /// Detail-Ansicht angezeigt.
+  final int erpCustomerId;
+  final Address address;
+
+  Customer copyWith({
+    String? id,
+    String? name,
+    int? erpCustomerId,
+    Address? address,
+  }) {
+    return Customer(
+      id: id ?? this.id,
+      name: name ?? this.name,
+      erpCustomerId: erpCustomerId ?? this.erpCustomerId,
+      address: address ?? this.address,
+    );
+  }
+}
+
+/// Ansprechpartner zu einem Kunden. Optional, daher als eigene Liste in
+/// `TourDetails` — eine Lieferung referenziert n Kontakte per Id.
+class CustomerContact {
+  const CustomerContact({
+    required this.id,
+    required this.customerId,
+    required this.name,
+    this.phone,
+    this.email,
+  });
+
+  final String id;
+  final String customerId;
+  final String name;
+  final String? phone;
+  final String? email;
+}