generated-scene: add scheduled monitoring runtime and helper lifecycle hardening

tests/scene_generator_modes_test.rs

@@ -96,6 +96,7 @@ fn make_test_scene_ir(modes: Vec<ModeIr>) -> SceneIr {
         column_defs: Vec::new(),
         confidence: 0.0,
         uncertainties: Vec::new(),
+        monitoring_action_workflow: None,
     }
 }