Add control gallery sample and roadmap documentation

- Add comprehensive ControlGallery sample app with 12 pages
  demonstrating all 35+ controls
- Add detailed ROADMAP.md with version milestones
- Add README placeholders for VSIX icons and template images
- Sample pages include: Home, Buttons, Labels, Entry, Pickers,
  Sliders, Toggles, Progress, Images, CollectionView, CarouselView,
  SwipeView, RefreshView

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

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

samples/ControlGallery/MauiProgram.cs

@@ -0,0 +1,22 @@
+using Microsoft.Maui.Hosting;
+using OpenMaui.Platform.Linux.Hosting;
+
+namespace ControlGallery;
+
+public static class MauiProgram
+{
+    public static MauiApp CreateMauiApp()
+    {
+        var builder = MauiApp.CreateBuilder();
+        builder
+            .UseMauiApp<App>()
+            .UseOpenMauiLinux()
+            .ConfigureFonts(fonts =>
+            {
+                fonts.AddFont("OpenSans-Regular.ttf", "OpenSansRegular");
+                fonts.AddFont("OpenSans-Semibold.ttf", "OpenSansSemibold");
+            });
+
+        return builder.Build();
+    }
+}