Refine Function Composition visualization: improve accessibility and clean up code

Author: myoshi2891

JavaScript/2629. Function Composition/Claude Code Sonnet 4.6 extended/README_react.html

@@ -1162,11 +1162,6 @@ <h3 class="text-lg font-bold text-[#e53170] mb-3">入出力例</h3>
 
                 useEffect(() => {
                     if (isPlaying) {
-                        if (activeStep > stepsData.length) {
-                            setIsPlaying(false);
-                            setActiveStep(1);
-                            return;
-                        }
                         timerRef.current = setTimeout(() => {
                             if (activeStep === stepsData.length) {
                                 setActiveStep(1);
@@ -1237,7 +1232,11 @@ <h3 className="text-lg font-bold text-[#e53170] mb-4">ステップ一覧</h3>
 
                         {/* Right: visualization */}
                         <div>
-                            <div className="rounded-2xl p-5 border border-[#e53170]/20 bg-[#0f0e17]">
+                            <div
+                                className="rounded-2xl p-5 border border-[#e53170]/20 bg-[#0f0e17]"
+                                aria-live="polite"
+                                aria-atomic="true"
+                            >
                                 <div className="text-[#e53170] mono text-xs font-semibold mb-1">
                                     Step {current.step} / {stepsData.length}
                                 </div>