feat(srp): add shader pass selection for scene draws

- let DrawingSettings carry an optional shaderPassName across managed and native scene draw APIs
- allow RenderObjectsRendererFeature to author explicit ForwardLit or Unlit scene draws
- exercise the new scene draw pass selection seam in the project render pipeline probe

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

@@ -107,6 +107,8 @@ namespace XCEngine.Rendering
                     (int)scenePhase,
                     ref rendererListDesc,
                     drawingSettings.overrideMaterialPath ??
+                        string.Empty,
+                    drawingSettings.shaderPassName ??
                         string.Empty);
         }