feat(01-06): build WPF shell — MainWindow XAML, ViewModels, LogPanelSink wiring

- Add FeatureTabBase UserControl with ProgressBar/TextBlock/CancelButton strip
  (Visibility bound to IsRunning, shown only during operations)
- Add MainWindowViewModel with TenantProfiles ObservableCollection, ConnectCommand,
  ClearSessionCommand, ManageProfilesCommand, ProgressUpdatedMessage subscription
- Add ProfileManagementViewModel wrapping ProfileService CRUD with input validation
- Add SettingsViewModel (extends FeatureViewModelBase) with language/folder settings
- Update MainWindow.xaml: DockPanel shell with Toolbar, TabControl (8 tabs), 150px
  RichTextBox LogPanel, StatusBar (tenant name | ProgressStatus | ProgressPercentage)
- MainWindow.xaml.cs: DI constructor, DataContext=viewModel, LoadProfilesAsync on Loaded
- App.xaml.cs: register all services, wire LogPanelSink after MainWindow resolved,
  register DispatcherUnhandledException and UnobservedTaskException global handlers
- App.xaml: add BoolToVisibilityConverter resource

SharepointToolbox/App.xaml.cs

@@ -1,13 +1,17 @@
+using System.IO;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
 using Serilog;
+using SharepointToolbox.Infrastructure.Auth;
+using SharepointToolbox.Infrastructure.Logging;
+using SharepointToolbox.Services;
+using SharepointToolbox.ViewModels;
+using SharepointToolbox.ViewModels.Tabs;
 using System.Windows;
 
 namespace SharepointToolbox;
 
-/// <summary>
-/// Interaction logic for App.xaml
-/// </summary>
 public partial class App : Application
 {
     [STAThread]
@@ -16,7 +20,7 @@ public partial class App : Application
         using IHost host = Host.CreateDefaultBuilder(args)
             .UseSerilog((ctx, cfg) => cfg
                 .WriteTo.File(
-                    System.IO.Path.Combine(
+                    Path.Combine(
                         Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
                         "SharepointToolbox", "logs", "app-.log"),
                     rollingInterval: RollingInterval.Day,
@@ -27,16 +31,49 @@ public partial class App : Application
         host.Start();
         App app = new();
         app.InitializeComponent();
-        app.MainWindow = host.Services.GetRequiredService<MainWindow>();
+
+        var mainWindow = host.Services.GetRequiredService<MainWindow>();
+
+        // Wire LogPanelSink now that we have the RichTextBox
+        Log.Logger = new LoggerConfiguration()
+            .WriteTo.File(
+                Path.Combine(
+                    Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData),
+                    "SharepointToolbox", "logs", "app-.log"),
+                rollingInterval: RollingInterval.Day,
+                retainedFileCountLimit: 30)
+            .WriteTo.Sink(new LogPanelSink(mainWindow.GetLogPanel()))
+            .CreateLogger();
+
+        // Global exception handlers
+        app.DispatcherUnhandledException += (s, e) =>
+        {
+            Log.Fatal(e.Exception, "Unhandled UI exception");
+            MessageBox.Show(
+                $"A fatal error occurred:\n{e.Exception.Message}\n\nCheck log for details.",
+                "Fatal Error", MessageBoxButton.OK, MessageBoxImage.Error);
+            e.Handled = true;
+        };
+        TaskScheduler.UnobservedTaskException += (s, e) =>
+        {
+            Log.Fatal(e.Exception, "Unobserved task exception");
+            e.SetObserved();
+        };
+
+        app.MainWindow = mainWindow;
         app.MainWindow.Visibility = Visibility.Visible;
         app.Run();
     }
 
     private static void RegisterServices(HostBuilderContext ctx, IServiceCollection services)
     {
-        // Placeholder — services registered in subsequent plans
+        services.AddSingleton<MsalClientFactory>();
+        services.AddSingleton<SessionManager>();
+        services.AddSingleton<ProfileService>();
+        services.AddSingleton<SettingsService>();
+        services.AddSingleton<MainWindowViewModel>();
+        services.AddTransient<ProfileManagementViewModel>();
+        services.AddTransient<SettingsViewModel>();
         services.AddSingleton<MainWindow>();
-        // LogPanelSink registered in plan 01-06 after MainWindow is created
-        // (requires RichTextBox reference from MainWindow)
     }
 }