debug: add ELK root layout logging to diagnose Y-offset issue

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cameleer3-server-app/src/main/java/com/cameleer3/server/app/diagram/ElkDiagramRenderer.java

@@ -284,6 +284,15 @@ public class ElkDiagramRenderer implements DiagramRenderer {
         RecursiveGraphLayoutEngine engine = new RecursiveGraphLayoutEngine();
         engine.layout(rootNode, new BasicProgressMonitor());
 
+        // Debug: log root dimensions and children
+        System.out.println("[ELK DEBUG] rootNode: " + rootNode.getWidth() + "x" + rootNode.getHeight()
+                + " children=" + rootNode.getChildren().size());
+        for (ElkNode child : rootNode.getChildren()) {
+            System.out.println("[ELK DEBUG]   child " + child.getIdentifier()
+                    + " x=" + child.getX() + " y=" + child.getY()
+                    + " w=" + child.getWidth() + " h=" + child.getHeight());
+        }
+
         // Run layout — each handler section independently
         for (ElkNode handlerRoot : handlerRoots) {
             engine.layout(handlerRoot, new BasicProgressMonitor());