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>
 

src/App/Views/MainWindow.axaml

@@ -7,7 +7,7 @@
         mc:Ignorable="d" d:DesignWidth="900" d:DesignHeight="620"
         x:Class="PalladiumWallet.App.Views.MainWindow"
         x:DataType="vm:MainWindowViewModel"
-        Icon="/Assets/avalonia-logo.ico"
+        Icon="/Assets/logo.ico"
         Width="900" Height="620"
         Title="Palladium Wallet">