feat(app): replace placeholder icon with Palladium Wallet logo

Add logo.png (source) and logo.ico (multi-size: 256/128/64/48/32/16)
generated with Pillow. Remove avalonia-logo.ico (Avalonia template
placeholder). Update MainWindow.axaml Icon and csproj ApplicationIcon
to point to the new files.

src/App/PalladiumWallet.App.csproj

@@ -4,6 +4,7 @@
     <TargetFramework>net8.0</TargetFramework>
     <Nullable>enable</Nullable>
     <ApplicationManifest>app.manifest</ApplicationManifest>
+    <ApplicationIcon>Assets\logo.ico</ApplicationIcon>
     <AvaloniaUseCompiledBindingsByDefault>true</AvaloniaUseCompiledBindingsByDefault>
   </PropertyGroup>
 
@@ -25,7 +26,7 @@
     <PackageReference Include="QRCoder" Version="1.8.0" />
   </ItemGroup>
 
-  <ItemGroup>
-    <ProjectReference Include="..\Core\PalladiumWallet.Core.csproj" />
+  <ItemGroup>
+    <ProjectReference Include="..\Core\PalladiumWallet.Core.csproj" />
   </ItemGroup>
 </Project>