feat(core): prepare typed Scenario layout and source lifecycle

crates/oa-desktop/src/forms.rs

@@ -1535,7 +1535,8 @@ fn group_label(path: &str) -> Option<&'static str> {
 }
 
 fn placement_allowed(project: &Project, diagram: &Diagram, element: &Element, current: Id) -> bool {
-    (diagram.projection == ProjectionKind::Traceability || diagram.layer == element.layer())
+    diagram.projection.scenario().is_none()
+        && (diagram.projection == ProjectionKind::Traceability || diagram.layer == element.layer())
         && diagram
             .projection
             .state_machine()
@@ -2683,6 +2684,7 @@ mod tests {
                 description: String::new(),
                 layer: Layer::Oa,
                 projection: ProjectionKind::Overview,
+                layout: None,
                 routes: Vec::new(),
                 view_options: Default::default(),
                 nodes: BTreeMap::new(),