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/CollectionViewPage.xaml

@@ -0,0 +1,47 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="ControlGallery.Pages.CollectionViewPage"
+             Title="CollectionView">
+
+    <Grid RowDefinitions="Auto,*">
+
+        <VerticalStackLayout Padding="20" Spacing="10">
+            <Label Text="CollectionView" FontSize="24" FontAttributes="Bold" />
+            <Label Text="Displaying a list of items with custom templates" TextColor="{StaticResource Gray500}" />
+        </VerticalStackLayout>
+
+        <CollectionView Grid.Row="1" x:Name="ItemsCollection" SelectionMode="Single" SelectionChanged="OnSelectionChanged">
+            <CollectionView.ItemTemplate>
+                <DataTemplate>
+                    <Frame Margin="10,5" Padding="15" CornerRadius="8">
+                        <Grid ColumnDefinitions="50,*,Auto">
+                            <BoxView WidthRequest="40"
+                                     HeightRequest="40"
+                                     Color="{Binding Color}"
+                                     CornerRadius="20" />
+
+                            <VerticalStackLayout Grid.Column="1" Margin="15,0" VerticalOptions="Center">
+                                <Label Text="{Binding Title}" FontAttributes="Bold" />
+                                <Label Text="{Binding Description}" TextColor="{StaticResource Gray500}" FontSize="12" />
+                            </VerticalStackLayout>
+
+                            <Label Grid.Column="2"
+                                   Text="{Binding Price, StringFormat='{0:C}'}"
+                                   FontAttributes="Bold"
+                                   VerticalOptions="Center" />
+                        </Grid>
+                    </Frame>
+                </DataTemplate>
+            </CollectionView.ItemTemplate>
+
+            <CollectionView.EmptyView>
+                <VerticalStackLayout HorizontalOptions="Center" VerticalOptions="Center">
+                    <Label Text="No items found" FontSize="18" TextColor="{StaticResource Gray400}" />
+                </VerticalStackLayout>
+            </CollectionView.EmptyView>
+        </CollectionView>
+
+    </Grid>
+
+</ContentPage>