feat: implement Story 3.2 — AI diagram generation from natural language

Add complete AI-powered diagram generation pipeline: natural language input
→ type inference → graph patch generation → validated canvas render with
ELK.js layout animation. Includes adversarial code review fixes for
diagramType enum validation, duplicate ID detection, tool part history
preservation, PATCH error handling, and graphData structural validation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/src/modules/diagram/hooks/useAutoLayout.ts

@@ -139,6 +139,15 @@ export function useAutoLayout() {
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [layoutDirection, edgeRouting]);
 
+  // Re-layout on explicit request (e.g., AI-generated graph patch)
+  const layoutRequestId = useGraphStore((s) => s.layoutRequestId);
+  useEffect(() => {
+    if (layoutRequestId > 0 && nodeCount > 0) {
+      runLayout();
+    }
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [layoutRequestId]);
+
   // Cleanup worker on unmount
   useEffect(() => {
     return () => {