fix(web): auto-detect browser language for live demo speech recognition (#166)

Use navigator.language instead of hardcoded 'en-US' so the demo works
for users with non-English browser settings (French, German, Spanish, etc.)

Fixes #165

web/src/components/live-demo.tsx

@@ -66,7 +66,7 @@ export function LiveDemo() {
         const recognition = new SpeechRecognitionAPI();
         recognition.continuous = true;
         recognition.interimResults = true;
-        recognition.lang = "en-US";
+        recognition.lang = navigator.language || "en-US";
 
         recognition.onstart = () => {
             setIsListening(true);