Avalonia shell: wire NewWindowRequested (and clear CS0067)

target=_blank / window.open requests are now suppressed and routed through
HandleLinkClick (open http(s) in the OS browser, follow local Markdown links
in-place), using WebViewNewWindowRequestedEventArgs.Request. The Avalonia
project now builds with 0 warnings. Smoke still green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: yotsuda

MarkdownPointer.Avalonia/AvaloniaWebViewHost.cs

@@ -28,8 +28,14 @@ public AvaloniaWebViewHost(NativeWebView webView)
 
         _webView.NavigationCompleted += (_, _) => NavigationCompleted?.Invoke();
 
-        // NewWindowRequested wiring deferred until the per-OS hosts are verified
-        // (arg shape differs); the minimal scaffold does not need it.
+        // target=_blank / window.open: suppress the popup and let the app decide
+        // (open in the OS browser, or follow a local Markdown link in-place).
+        _webView.NewWindowRequested += (_, e) =>
+        {
+            e.Handled = true;
+            if (e.Request is { } uri)
+                NewWindowRequested?.Invoke(uri.ToString());
+        };
     }
 
     public object Control => _webView;

MarkdownPointer.Avalonia/MainWindow.axaml.cs

@@ -46,6 +46,7 @@ public MainWindow()
         _host = new AvaloniaWebViewHost(_webView);
         _host.MessageReceived += OnHostMessage;
         _host.NavigationCompleted += OnNavigationCompleted;
+        _host.NewWindowRequested += HandleLinkClick;   // target=_blank / window.open
 
         Loaded += (_, _) => { Render(); SetupWatcher(); };
         Closed += (_, _) => { _watcher?.Dispose(); _reloadDebounce?.Stop(); };