rendering: document managed srp v1 boundaries

managed/XCEngine.ScriptCore/Rendering/Core/RenderSceneSetupContext.cs

@@ -1,5 +1,7 @@
 namespace XCEngine.Rendering
 {
+    // Managed hook for scene-setup policy only. Scene extraction, culling, and
+    // the actual scene draws still execute through the native backend.
     public sealed class RenderSceneSetupContext
     {
         private readonly ulong m_nativeHandle;