fix(graphrag): graph view rendered blank — measure container after load

The ResizeObserver/size effect ran once on mount with [] deps while loading=true, so containerRef was null (the graph container isn't in the DOM yet) and size.width stayed 0, gating out ForceGraph2D (blank canvas) even though the data loaded. Re-run the measure effect on [loading, data.nodes.length] so it attaches + measures once the container actually mounts.

frontend/src/components/GraphView.tsx

@@ -78,7 +78,7 @@ const GraphView: React.FC<GraphViewProps> = ({
     observer.observe(element);
     setSize({ width: element.clientWidth, height: 480 });
     return () => observer.disconnect();
-  }, []);
+  }, [loading, data.nodes.length]);
 
   const maxNodeDegree = useMemo(() => maxDegree(data.nodes), [data.nodes]);