Add WebView support via WebKitGTK

Implements Priority 4 item: WebView via WebKitGTK

New files:
- Interop/WebKitGtk.cs - P/Invoke bindings for WebKitGTK library
- Views/LinuxWebView.cs - WebKitGTK-based WebView platform control
- Handlers/WebViewHandler.Linux.cs - MAUI handler for WebView on Linux
- samples_temp/WebViewDemo/ - Demo app for WebView functionality

Features:
- Full HTML5/CSS3/JavaScript support via WebKitGTK
- Navigation (back/forward/reload)
- URL and HTML source loading
- JavaScript evaluation
- Navigation events (Navigating/Navigated)
- Automatic GTK event processing

Requirements:
- libwebkit2gtk-4.1-0 package on target Linux system

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

samples_temp/ShellDemo/App.cs

@@ -0,0 +1,78 @@
+// ShellDemo App - Comprehensive Control Demo
+
+using Microsoft.Maui.Controls;
+
+namespace ShellDemo;
+
+/// <summary>
+/// Main application class with Shell navigation.
+/// </summary>
+public class App : Application
+{
+    public App()
+    {
+        MainPage = new AppShell();
+    }
+}
+
+/// <summary>
+/// Shell definition with flyout menu - comprehensive control demo.
+/// </summary>
+public class AppShell : Shell
+{
+    public AppShell()
+    {
+        FlyoutBehavior = FlyoutBehavior.Flyout;
+        Title = "OpenMaui Controls Demo";
+
+        // Register routes for push navigation (pages not in flyout)
+        Routing.RegisterRoute("detail", typeof(DetailPage));
+
+        // Home
+        Items.Add(CreateFlyoutItem("Home", typeof(HomePage)));
+
+        // Buttons Demo
+        Items.Add(CreateFlyoutItem("Buttons", typeof(ButtonsPage)));
+
+        // Text Input Demo
+        Items.Add(CreateFlyoutItem("Text Input", typeof(TextInputPage)));
+
+        // Selection Controls Demo
+        Items.Add(CreateFlyoutItem("Selection", typeof(SelectionPage)));
+
+        // Pickers Demo
+        Items.Add(CreateFlyoutItem("Pickers", typeof(PickersPage)));
+
+        // Lists Demo
+        Items.Add(CreateFlyoutItem("Lists", typeof(ListsPage)));
+
+        // Progress Demo
+        Items.Add(CreateFlyoutItem("Progress", typeof(ProgressPage)));
+
+        // Grids Demo
+        Items.Add(CreateFlyoutItem("Grids", typeof(GridsPage)));
+
+        // About
+        Items.Add(CreateFlyoutItem("About", typeof(AboutPage)));
+    }
+
+    private FlyoutItem CreateFlyoutItem(string title, Type pageType)
+    {
+        // Route is required for Shell.GoToAsync navigation to work
+        var route = title.Replace(" ", "");
+        return new FlyoutItem
+        {
+            Title = title,
+            Route = route,
+            Items =
+            {
+                new ShellContent
+                {
+                    Title = title,
+                    Route = route,
+                    ContentTemplate = new DataTemplate(pageType)
+                }
+            }
+        };
+    }
+}