refactor(fit-app): drop macOS Dock P/Invoke; address review comments

Samples must not use unmanaged code. Remove the AppKit P/Invoke Dock-icon path
(MacOSDockIcon.cs, App.Desktop.cs, DockIcon.png + its wiring in App.xaml.cs and
the csproj). The branded icon still ships via Uno.Resizetizer — the app icon on
every platform, and the packaged macOS .app shows it in the Dock; the generic
tile on an unbundled `dotnet run` is an accepted dev-only cosmetic limitation.

Also dispose the previous PathGeometry before replacing it in
WeeklyRing.UpdateArc (flagged by review).

Addresses the github-code-quality review on #930.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Jen-Uno

studio/fit-app/FitBeginnerApp/App.xaml.cs

@@ -87,15 +87,8 @@ protected async override void OnLaunched(LaunchActivatedEventArgs args)
                 MainWindow.SetWindowIcon();
 
         Host = await builder.NavigateAsync<Shell>();
-
-        // On the macOS desktop (Skia) head, brand the Dock during an unbundled dev run; the partial
-        // method is implemented only in Platforms/Desktop and is elided (a no-op) on every other head.
-        TrySetDesktopDockIcon();
     }
 
-    // Implemented in Platforms/Desktop/App.Desktop.cs; elided on the iOS / Android / WebAssembly heads.
-    partial void TrySetDesktopDockIcon();
-
     private static void RegisterRoutes(IViewRegistry views, IRouteRegistry routes)
     {
         views.Register(

studio/fit-app/FitBeginnerApp/FitBeginnerApp.csproj

@@ -61,15 +61,4 @@
     <Content Include="Assets/Fonts/Montserrat-Bold.ttf" />
   </ItemGroup>
 
-  <!--
-    macOS Dock icon (Skia desktop head only): a pre-baked rounded "squircle" macOS-grid PNG, copied
-    next to the executable so Platforms/Desktop/App.Desktop.cs can hand its path to
-    NSApplication.applicationIconImage during a dev run. macOS does not mask applicationIconImage, so
-    the rounded grid is baked in; it was rasterized from the app's Resizetizer icon assets. Other
-    platforms/OSes never use it.
-  -->
-  <ItemGroup Condition="'$(TargetFramework)' == 'net10.0-desktop'">
-    <Content Include="Platforms/Desktop/DockIcon.png" Link="DockIcon.png" CopyToOutputDirectory="PreserveNewest" />
-  </ItemGroup>
-
 </Project>

studio/fit-app/FitBeginnerApp/Platforms/Desktop/App.Desktop.cs

@@ -134,6 +134,8 @@ private void UpdateArc()
         var fraction = Math.Clamp(Progress, 0, 1);
         if (fraction <= 0)
         {
+            // Release the native geometry backing the old arc before detaching it.
+            (ArcPath.Data as IDisposable)?.Dispose();
             ArcPath.Data = null;
             return;
         }
@@ -161,6 +163,9 @@ private void UpdateArc()
 
         var geometry = new PathGeometry();
         geometry.Figures.Add(figure);
+        // Dispose the geometry from the previous update before it is replaced (UpdateArc runs on
+        // every progress tick during the entrance animation, so a fresh geometry is built each time).
+        (ArcPath.Data as IDisposable)?.Dispose();
         ArcPath.Data = geometry;
     }