Add Avalonia server-host launcher (MVP scaffold)

Cross-platform C# GUI to replace the Qt/C++ Host GUI, on the same dotnet
toolchain as the server. MVP: load/save commonwealth-server.json, Start/Stop
the CommonwealthOnline.Server process (published exe, then dll, then source
run), and stream its output to a live log. Themed to the Commonwealth Online
brand (near-black + amber). Builds clean on net8.0.

Next: player list + kick/ban via the admin port, then retire the Qt host.

host/CommonwealthOnline.Host.csproj

@@ -0,0 +1,26 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>WinExe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <Nullable>enable</Nullable>
+    <LangVersion>latest</LangVersion>
+    <BuiltInComInteropSupport>true</BuiltInComInteropSupport>
+    <AvaloniaUseCompiledBindingsByDefault>false</AvaloniaUseCompiledBindingsByDefault>
+    <AssemblyName>CommonwealthOnline.Host</AssemblyName>
+    <RootNamespace>CommonwealthOnline.Host</RootNamespace>
+    <ApplicationIcon></ApplicationIcon>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <AvaloniaResource Include="Assets/**" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Avalonia" Version="11.1.0" />
+    <PackageReference Include="Avalonia.Desktop" Version="11.1.0" />
+    <PackageReference Include="Avalonia.Themes.Fluent" Version="11.1.0" />
+    <PackageReference Include="CommunityToolkit.Mvvm" Version="8.2.2" />
+  </ItemGroup>
+
+</Project>