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/Pages/CarouselViewPage.xaml.cs

@@ -0,0 +1,70 @@
+namespace ControlGallery.Pages;
+
+public partial class CarouselViewPage : ContentPage
+{
+    private readonly List<CarouselItem> _items;
+
+    public CarouselViewPage()
+    {
+        InitializeComponent();
+
+        _items = new List<CarouselItem>
+        {
+            new() { Title = "Welcome", Description = "Get started with OpenMaui", Icon = "👋", Color = Color.FromArgb("#512BD4") },
+            new() { Title = "Controls", Description = "35+ beautiful controls", Icon = "🎨", Color = Color.FromArgb("#2196F3") },
+            new() { Title = "Native", Description = "X11 & Wayland support", Icon = "🐧", Color = Color.FromArgb("#4CAF50") },
+            new() { Title = "Fast", Description = "Hardware accelerated", Icon = "⚡", Color = Color.FromArgb("#FF9800") },
+            new() { Title = "Accessible", Description = "Screen reader support", Icon = "♿", Color = Color.FromArgb("#9C27B0") },
+        };
+
+        Carousel.ItemsSource = _items;
+        Carousel.IndicatorView = CarouselIndicator;
+
+        UpdateCurrentItemLabel();
+    }
+
+    private void OnCurrentItemChanged(object sender, CurrentItemChangedEventArgs e)
+    {
+        UpdateCurrentItemLabel();
+    }
+
+    private void UpdateCurrentItemLabel()
+    {
+        var index = _items.IndexOf(Carousel.CurrentItem as CarouselItem);
+        CurrentItemLabel.Text = $"Slide {index + 1} of {_items.Count}";
+    }
+
+    private void OnPreviousClicked(object sender, EventArgs e)
+    {
+        var index = _items.IndexOf(Carousel.CurrentItem as CarouselItem);
+        if (index > 0)
+        {
+            Carousel.ScrollTo(index - 1);
+        }
+        else
+        {
+            Carousel.ScrollTo(_items.Count - 1);
+        }
+    }
+
+    private void OnNextClicked(object sender, EventArgs e)
+    {
+        var index = _items.IndexOf(Carousel.CurrentItem as CarouselItem);
+        if (index < _items.Count - 1)
+        {
+            Carousel.ScrollTo(index + 1);
+        }
+        else
+        {
+            Carousel.ScrollTo(0);
+        }
+    }
+}
+
+public class CarouselItem
+{
+    public string Title { get; set; } = string.Empty;
+    public string Description { get; set; } = string.Empty;
+    public string Icon { get; set; } = string.Empty;
+    public Color Color { get; set; } = Colors.Gray;
+}