Phase 1: versioning, menu bar, About dialog, right-click context menu

- Directory.Build.props sets Version=0.1.0 (semver pre-1.0 = beta) plus
  Authors / Product / RepositoryUrl, picked up by all three projects.
- MainWindow gets a real menu bar (File / Server / Help) replacing the
  old toolbar. File: New endpoint / Import / Export / Backups (last
  three are stubs for the next phase) / Exit. Server: Settings /
  Restart service. Help: About.
- Drop the Refresh button - the 3 s polling loop covers it.
- DataGridRow gets a right-click context menu: Edit / Copy URL /
  toggle Enabled / Delete.
- New About dialog reads AssemblyInformationalVersion at runtime and
  links jpaul.me + the GitHub repo via clickable hyperlinks.
- Ctrl+N input binding for new-endpoint.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/WebhookServer.Gui/Views/AboutDialog.xaml.cs

@@ -0,0 +1,28 @@
+using System.Diagnostics;
+using System.Reflection;
+using System.Windows;
+using System.Windows.Navigation;
+
+namespace WebhookServer.Gui.Views;
+
+public partial class AboutDialog : Window
+{
+    public AboutDialog()
+    {
+        InitializeComponent();
+
+        var asm = Assembly.GetExecutingAssembly();
+        var info = asm.GetCustomAttribute<AssemblyInformationalVersionAttribute>()?.InformationalVersion
+                   ?? asm.GetName().Version?.ToString()
+                   ?? "0.0.0";
+        VersionText.Text = $"Version {info}";
+    }
+
+    private void OnHyperlink(object sender, RequestNavigateEventArgs e)
+    {
+        Process.Start(new ProcessStartInfo(e.Uri.AbsoluteUri) { UseShellExecute = true });
+        e.Handled = true;
+    }
+
+    private void OnOk(object sender, RoutedEventArgs e) => Close();
+}