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>

templates/openmaui-linux-xaml-app/Resources/Images/README.md

@@ -0,0 +1,22 @@
+# Image Resources
+
+## Required Images
+
+### dotnet_bot.png
+Download from the official .NET MAUI repository:
+https://github.com/dotnet/maui/blob/main/src/Templates/src/templates/maui-mobile/Resources/Images/dotnet_bot.png
+
+Or use your own application icon.
+
+## Adding Images
+
+Place images in this folder and reference them in XAML:
+
+```xml
+<Image Source="dotnet_bot.png" WidthRequest="250" HeightRequest="310" />
+```
+
+Images are automatically included via the project file:
+```xml
+<MauiImage Include="Resources\Images\*" />
+```