Initial setup: Fix target framework for sample project compatibility

Co-authored-by: lucafabbri <12503462+lucafabbri@users.noreply.github.com>

Author: Copilot

ProjectR.Sample/ProjectR.Sample.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk.Web">
 
   <PropertyGroup>
-    <TargetFramework>net9.0</TargetFramework>
+    <TargetFramework>net8.0</TargetFramework>
     <Nullable>enable</Nullable>
     <ImplicitUsings>enable</ImplicitUsings>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>