fix: scrollable headers/timeline, CodeBlock for body, ELK node alignment

- Make headers tab and timeline tab scrollable when content overflows
- Replace custom <pre> code block with design system CodeBlock component
  for body tabs (Input/Output) to match existing styleguide
- Add LINEAR_SEGMENTS node placement strategy to ELK layout to fix
  Y-offset misalignment between nodes in left-to-right diagrams
  (e.g., ENDPOINT at different Y level than subsequent processors)

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

@@ -13,6 +13,7 @@ import org.eclipse.elk.core.RecursiveGraphLayoutEngine;
 import org.eclipse.elk.core.options.CoreOptions;
 import org.eclipse.elk.core.options.Direction;
 import org.eclipse.elk.core.options.HierarchyHandling;
+import org.eclipse.elk.alg.layered.options.NodePlacementStrategy;
 import org.eclipse.elk.core.util.BasicProgressMonitor;
 import org.eclipse.elk.graph.ElkBendPoint;
 import org.eclipse.elk.graph.ElkEdge;
@@ -181,6 +182,8 @@ public class ElkDiagramRenderer implements DiagramRenderer {
         rootNode.setProperty(CoreOptions.SPACING_NODE_NODE, NODE_SPACING);
         rootNode.setProperty(CoreOptions.SPACING_EDGE_NODE, EDGE_SPACING);
         rootNode.setProperty(CoreOptions.HIERARCHY_HANDLING, HierarchyHandling.INCLUDE_CHILDREN);
+        rootNode.setProperty(org.eclipse.elk.alg.layered.options.LayeredOptions.NODE_PLACEMENT_STRATEGY,
+                NodePlacementStrategy.LINEAR_SEGMENTS);
 
         // Build index of all RouteNodes (flat list from graph + recursive children)
         Map<String, RouteNode> routeNodeMap = new HashMap<>();