feat(ui): use ClaudeTask icon for window and taskbar

Expose the .ico as an Avalonia resource, set it on MainWindow, and
swap the custom SystemDecorations=None for BorderOnly so the icon
appears on the taskbar and window can be resized normally.

src/ClaudeDo.Ui/ClaudeDo.Ui.csproj

@@ -22,6 +22,7 @@
     <AvaloniaResource Include="Assets/Fonts/*.ttf" />
     <AvaloniaResource Include="Assets/Fonts/OFL-InterTight.txt" />
     <AvaloniaResource Include="Assets/Fonts/OFL-JetBrainsMono.txt" />
+    <AvaloniaResource Include="..\ClaudeDo.App\Assets\ClaudeTask.ico" Link="Assets\ClaudeTask.ico" />
   </ItemGroup>
 
 </Project>

src/ClaudeDo.Ui/Views/MainWindow.axaml

@@ -7,7 +7,9 @@
         Title="ClaudeDo"
         Width="1280" Height="820" MinWidth="780" MinHeight="600"
         Background="{DynamicResource VoidBrush}"
-        SystemDecorations="None"
+        Icon="avares://ClaudeDo.Ui/Assets/ClaudeTask.ico"
+        CanResize="True"
+        SystemDecorations="BorderOnly"
         ExtendClientAreaToDecorationsHint="True"
         ExtendClientAreaTitleBarHeightHint="-1">
   <Window.KeyBindings>
@@ -26,11 +28,11 @@
         <!-- Left: brand block -->
         <StackPanel Grid.Column="0" Orientation="Horizontal" Spacing="8"
                     VerticalAlignment="Center" Margin="14,0,0,0">
-          <!-- Green checkbox glyph -->
-          <PathIcon Classes="title-brand-icon"
-                    Data="{StaticResource Icon.BrandCheck}"
-                    Width="14" Height="14"
-                    Foreground="{DynamicResource MossBrush}" />
+          <!-- App icon (matches taskbar) -->
+          <Image Source="avares://ClaudeDo.Ui/Assets/ClaudeTask.ico"
+                 Width="16" Height="16"
+                 VerticalAlignment="Center"
+                 RenderOptions.BitmapInterpolationMode="HighQuality"/>
           <!-- CLAUDEDO label -->
           <TextBlock Classes="title-brand-name"
                      Text="CLAUDEDO"