fix Alt+Left/Right browser navigation in simulator

The keyboard handler for stepping through flows was intercepting all
ArrowLeft/ArrowRight events, preventing browser back/forward. Now skips
when any modifier key (Alt, Ctrl, Meta) is held.

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

Author: dsshimel

attendabot/frontend/src/simulations/FlowDiagram.tsx

@@ -51,6 +51,7 @@ export default function FlowDiagram({ flow }: { flow: AuthFlow }) {
   // Keyboard shortcuts
   useEffect(() => {
     const handler = (e: KeyboardEvent) => {
+      if (e.altKey || e.ctrlKey || e.metaKey) return;
       if (e.key === "ArrowRight" || e.key === " ") {
         e.preventDefault();
         next();