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/LauncherService.cs

@@ -0,0 +1,85 @@
+// 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 launcher service for opening URLs and files.
+/// </summary>
+public class LauncherService : ILauncher
+{
+    public Task<bool> CanOpenAsync(Uri uri)
+    {
+        // On Linux, we can generally open any URI using xdg-open
+        return Task.FromResult(true);
+    }
+
+    public Task<bool> OpenAsync(Uri uri)
+    {
+        return Task.Run(() =>
+        {
+            try
+            {
+                var psi = new ProcessStartInfo
+                {
+                    FileName = "xdg-open",
+                    Arguments = uri.ToString(),
+                    UseShellExecute = false,
+                    RedirectStandardOutput = true,
+                    RedirectStandardError = true,
+                    CreateNoWindow = true
+                };
+
+                using var process = Process.Start(psi);
+                if (process == null)
+                    return false;
+
+                // Don't wait for the process to exit - xdg-open may spawn another process
+                return true;
+            }
+            catch
+            {
+                return false;
+            }
+        });
+    }
+
+    public Task<bool> OpenAsync(OpenFileRequest request)
+    {
+        if (request.File == null)
+            return Task.FromResult(false);
+
+        return Task.Run(() =>
+        {
+            try
+            {
+                var filePath = request.File.FullPath;
+
+                var psi = new ProcessStartInfo
+                {
+                    FileName = "xdg-open",
+                    Arguments = $"\"{filePath}\"",
+                    UseShellExecute = false,
+                    RedirectStandardOutput = true,
+                    RedirectStandardError = true,
+                    CreateNoWindow = true
+                };
+
+                using var process = Process.Start(psi);
+                return process != null;
+            }
+            catch
+            {
+                return false;
+            }
+        });
+    }
+
+    public Task<bool> TryOpenAsync(Uri uri)
+    {
+        return OpenAsync(uri);
+    }
+}