chore: scaffold progression domain + test projects (slice 0)

net8.0 classlib, no engine ref, EnableDynamicLoading; xunit test project
referencing domain only; excluded from Godot's **/*.cs glob; .gdignore both

Mr. Brick Adventures.csproj

@@ -9,4 +9,15 @@
     <PackageReference Include="Facepunch.Steamworks.Dlls" Version="2.3.2" />
     <PackageReference Include="Facepunch.Steamworks.Library" Version="2.3.3" />
   </ItemGroup>
+
+  <!-- Godot.NET.Sdk globs **/*.cs, which would compile the progression projects into this
+       assembly as well as their own. They are separate projects; exclude them here. -->
+  <ItemGroup>
+    <Compile Remove="progression\**" />
+    <Compile Remove="progression.tests\**" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="progression\Mr.BrickAdventures.Progression.csproj" />
+  </ItemGroup>
 </Project>