fix: revert Tests TFM to net8.0, fix WPF temp project ref resolution

- Revert Tests TFM back to net8.0 (test project references net8.0-windows
  Core library just fine, and this restores xunit implicit usings)
- Add IncludePackageReferencesDuringMarkupCompilation to App csproj
  to ensure NuGet/ProjectReference types resolve in WPF _wpftmp project

Author: SSDWGG

win/OneMenu.App/OneMenu.App.csproj

@@ -4,6 +4,7 @@
     <OutputType>WinExe</OutputType>
     <TargetFramework>net8.0-windows</TargetFramework>
     <UseWPF>true</UseWPF>
+    <IncludePackageReferencesDuringMarkupCompilation>true</IncludePackageReferencesDuringMarkupCompilation>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <RootNamespace>OneMenu.App</RootNamespace>

win/OneMenu.Tests/OneMenu.Tests.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net8.0-windows</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
     <IsTestProject>true</IsTestProject>