feat: move test buttons to right panel, add user auth dialog for reports

Move Start/Stop/Report buttons from the middle panel to the top of
TestPanelView (automated tests section), matching the old application
layout. Remove inline Operator/Client text fields — operator identity
now comes from a UserCheckDialog (username/password) shown before the
existing ReportDialog. Add credential storage to ConfigurationService.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Views/Dialogs/UserCheckDialog.xaml.cs

@@ -0,0 +1,30 @@
+using System.Windows;
+using System.Windows.Controls;
+using HC_APTBS.ViewModels.Dialogs;
+
+namespace HC_APTBS.Views.Dialogs
+{
+    /// <summary>
+    /// Authentication dialog that collects username and password before report generation.
+    /// </summary>
+    public partial class UserCheckDialog : Window
+    {
+        /// <summary>Creates the dialog and wires the ViewModel.</summary>
+        public UserCheckDialog(UserCheckViewModel vm)
+        {
+            InitializeComponent();
+            DataContext = vm;
+            vm.RequestClose += Close;
+        }
+
+        /// <summary>
+        /// Forwards the PasswordBox value to the ViewModel.
+        /// WPF intentionally does not expose Password as a DependencyProperty.
+        /// </summary>
+        private void OnPasswordChanged(object sender, RoutedEventArgs e)
+        {
+            if (DataContext is UserCheckViewModel vm)
+                vm.Password = ((PasswordBox)sender).Password;
+        }
+    }
+}