[fix:] make customer delete button working

MainWindow.axaml

@@ -509,7 +509,7 @@
                                                    VerticalContentAlignment="Center" />
                                         </StackPanel>
                                     </Button>
-                                    <Button Background="#99963434" HorizontalAlignment="Stretch"
+                                    <Button Background="#99963434" HorizontalAlignment="Stretch" x:Name="BtnDeleteCustomer" Click="BtnDeleteCustomer_OnClick"
                                             HorizontalContentAlignment="Center">
                                         <StackPanel Orientation="Horizontal">
                                             <LucideIcon Kind="Trash" Width="16" Height="16" Size="16" />

MainWindow.axaml.cs

@@ -1128,4 +1128,21 @@ public partial class MainWindow : Window
                 MessageBox.Show(this, ex.StackTrace, "Fehler");
             }
     }
+
+    private void BtnDeleteCustomer_OnClick(object? sender, RoutedEventArgs e)
+    {
+        if (LstSettingsCustomers.SelectedIndex == null || LstSettingsCustomers.SelectedIndex == -1) return;
+        foreach (var customer in Settings._instance.customers.customers)
+            if (customer.ID == Settings._instance.customers.current)
+                try
+                {
+                    Settings._instance.customers.customers.Remove(customer);
+                    break;
+                }
+                catch (Exception ex)
+                {
+                    MessageBox.Show(this, "Unknown Error: " + ex.Message, "Error");
+                }
+        RefreshCustomerItems();
+    }
 }