perf: short-circuit allNodes useMemo when no dimming is active

When dimmedNodeIds is empty and no node has a stale switch-dimmed class,
return the nodes array directly (same reference, zero iteration). The
.map() + regex only runs when dimming is actually active, which is the
uncommon case for most workflows.

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

src/components/WorkflowCanvas.tsx

@@ -331,6 +331,11 @@ export function WorkflowCanvas() {
 
   // Apply dimming className to nodes downstream of disabled Switch outputs
   const allNodes = useMemo(() => {
+    // Fast path: no dimming active and no stale dimmed classes to clean up
+    if (dimmedNodeIds.size === 0 && !nodes.some((n) => n.className?.includes("switch-dimmed"))) {
+      return nodes;
+    }
+
     return nodes.map((node) => {
       // Never dim Switch or ConditionalSwitch nodes themselves
       if (node.type === "switch" || node.type === "conditionalSwitch") return node;