fix: defer Sigma init with requestAnimationFrame to prevent no-height crash

Container has no computed height when useEffect fires immediately
after data arrives. Defer to next animation frame so browser layout
completes. Also add allowInvalidContainer as safety net.

src/pages/ReferralNetwork/components/NetworkGraph.tsx

@@ -128,6 +128,13 @@ export function NetworkGraph({ data, className }: NetworkGraphProps) {
   useEffect(() => {
     if (!containerRef.current || !data) return;
 
+    const container = containerRef.current;
+
+    // Defer initialization to next frame so the browser computes layout first.
+    // Without this, container.offsetHeight is 0 and Sigma throws.
+    const rafId = requestAnimationFrame(() => {
+      if (!container.isConnected) return;
+
       // Cleanup previous instance
       killFA2();
       if (sigmaRef.current) {
@@ -142,7 +149,8 @@ export function NetworkGraph({ data, className }: NetworkGraphProps) {
       const initialFilters = useReferralNetworkStore.getState().filters;
       hiddenNodesRef.current = computeHiddenNodes(graph, initialFilters);
 
-    const sigma = new Sigma(graph, containerRef.current, {
+      const sigma = new Sigma(graph, container, {
+        allowInvalidContainer: true,
         renderEdgeLabels: false,
         labelDensity: 0.5,
         labelRenderedSizeThreshold: 6,
@@ -289,11 +297,15 @@ export function NetworkGraph({ data, className }: NetworkGraphProps) {
           containerRef.current.style.cursor = 'default';
         }
       });
+    }); // end requestAnimationFrame
 
     return () => {
+      cancelAnimationFrame(rafId);
       killFA2();
-      sigma.kill();
+      if (sigmaRef.current) {
+        sigmaRef.current.kill();
         sigmaRef.current = null;
+      }
       graphRef.current = null;
       setSigmaInstance(null);
       setGraphInstance(null);