feat: add execution overlay types and extend ProcessDiagram with diagramLayout prop

Define the execution overlay type system (NodeExecutionState, IterationInfo,
DetailTab) and extend ProcessDiagramProps with optional overlay props. Add
diagramLayout prop so ExecutionDiagram can pass a pre-fetched layout by content
hash, bypassing the internal route-based fetch in useDiagramData.

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

ui/src/components/ProcessDiagram/ProcessDiagram.tsx

@@ -52,6 +52,7 @@ export function ProcessDiagram({
   nodeConfigs,
   knownRouteIds,
   className,
+  diagramLayout,
 }: ProcessDiagramProps) {
   // Route stack for drill-down navigation
   const [routeStack, setRouteStack] = useState<string[]>([routeId]);
@@ -64,7 +65,7 @@ export function ProcessDiagram({
   const currentRouteId = routeStack[routeStack.length - 1];
 
   const { sections, totalWidth, totalHeight, isLoading, error } = useDiagramData(
-    application, currentRouteId, direction,
+    application, currentRouteId, direction, diagramLayout,
   );
 
   const zoom = useZoomPan();