Enable onlyRenderVisibleElements in React Flow for performance

Skips rendering off-screen nodes and edges, reducing DOM size and
improving performance on large workflows.

https://claude.ai/code/session_01MvD1n4QeXutgwUpKJuDGHa

src/components/WorkflowCanvas.tsx

@@ -2012,6 +2012,7 @@ export function WorkflowCanvas() {
         nodesDraggable={!isModalOpen}
         nodesConnectable={!isModalOpen}
         elementsSelectable={!isModalOpen}
+        onlyRenderVisibleElements
         className="bg-neutral-900"
         proOptions={{ hideAttribution: true }}
         defaultEdgeOptions={{