Initial commit: .NET MAUI Linux Platform

Complete Linux platform implementation for .NET MAUI with:

- 35+ Skia-rendered controls (Button, Label, Entry, CarouselView, etc.)
- Platform services (Clipboard, FilePicker, Notifications, DragDrop, etc.)
- Accessibility support (AT-SPI2, High Contrast)
- HiDPI and Input Method support
- 216 unit tests
- CI/CD workflows
- Project templates
- Documentation

🤖 Generated with Claude Code

Services/BrowserService.cs

@@ -0,0 +1,66 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Diagnostics;
+using Microsoft.Maui.ApplicationModel;
+
+namespace Microsoft.Maui.Platform.Linux.Services;
+
+/// <summary>
+/// Linux browser implementation using xdg-open.
+/// </summary>
+public class BrowserService : IBrowser
+{
+    public async Task<bool> OpenAsync(string uri)
+    {
+        return await OpenAsync(new Uri(uri), BrowserLaunchMode.SystemPreferred);
+    }
+
+    public async Task<bool> OpenAsync(string uri, BrowserLaunchMode launchMode)
+    {
+        return await OpenAsync(new Uri(uri), launchMode);
+    }
+
+    public async Task<bool> OpenAsync(Uri uri)
+    {
+        return await OpenAsync(uri, BrowserLaunchMode.SystemPreferred);
+    }
+
+    public async Task<bool> OpenAsync(Uri uri, BrowserLaunchMode launchMode)
+    {
+        return await OpenAsync(uri, new BrowserLaunchOptions { LaunchMode = launchMode });
+    }
+
+    public async Task<bool> OpenAsync(Uri uri, BrowserLaunchOptions options)
+    {
+        if (uri == null)
+            throw new ArgumentNullException(nameof(uri));
+
+        try
+        {
+            var uriString = uri.AbsoluteUri;
+
+            // Use xdg-open which respects user's default browser
+            var startInfo = new ProcessStartInfo
+            {
+                FileName = "xdg-open",
+                Arguments = $"\"{uriString}\"",
+                UseShellExecute = false,
+                RedirectStandardOutput = true,
+                RedirectStandardError = true,
+                CreateNoWindow = true
+            };
+
+            using var process = Process.Start(startInfo);
+            if (process == null)
+                return false;
+
+            await process.WaitForExitAsync();
+            return process.ExitCode == 0;
+        }
+        catch
+        {
+            return false;
+        }
+    }
+}