Refactor engine architecture and project structure

Updated the organization of engine libraries to group features by architectural role rather than by individual feature. Enhanced documentation in CLAUDE.md and architecture.md to reflect these changes. Removed obsolete project references and added new modules for content management and simulation. Adjusted project files for MrGameEng.Graphics and MrGameEng.UI.Tests to align with the new structure.

This refactor aims to streamline the development process and improve clarity in the engine's architecture.

src/MrGameEng.Content/MrGameEng.Content.csproj

@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <InternalsVisibleTo Include="MrGameEng.Content.Tests" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="FontStashSharp.MonoGame" />
+    <PackageReference Include="StbImageSharp" />
+    <PackageReference Include="StbImageWriteSharp" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\MrGameEng.Core\MrGameEng.Core.csproj" />
+    <ProjectReference Include="..\MrGameEng.Graphics\MrGameEng.Graphics.csproj" />
+  </ItemGroup>
+</Project>

src/MrGameEng.Graphics/MrGameEng.Graphics.csproj

@@ -3,6 +3,10 @@
     <TargetFramework>net8.0</TargetFramework>
   </PropertyGroup>
 
+  <ItemGroup>
+    <InternalsVisibleTo Include="MrGameEng.Graphics.Tests" />
+  </ItemGroup>
+
   <ItemGroup>
     <ProjectReference Include="..\MrGameEng.Core\MrGameEng.Core.csproj" />
   </ItemGroup>

src/MrGameEng.Simulation/MrGameEng.Simulation.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\MrGameEng.Core\MrGameEng.Core.csproj" />
+    <ProjectReference Include="..\MrGameEng.Graphics\MrGameEng.Graphics.csproj" />
+  </ItemGroup>
+</Project>