perf(booth): optimize assets and result flow

WebP reduces UI payload; JPEG keeps portrait saves compatible.\nFinish ends the visit without prompting another portrait.

app/page.tsx

@@ -9,6 +9,7 @@ import { ConfirmScreen } from "@/components/screens/ConfirmScreen";
 import { StyleScreen } from "@/components/screens/StyleScreen";
 import { LoadingScreen } from "@/components/screens/LoadingScreen";
 import { ResultScreen } from "@/components/screens/ResultScreen";
+import { FinishedScreen } from "@/components/screens/FinishedScreen";
 import { RateLimitedScreen } from "@/components/screens/RateLimitedScreen";
 import { BoothConfig, BoothStyle, ScreenState } from "@/types/booth";
 import { I18nProvider, useI18n } from "@/lib/i18n";
@@ -50,9 +51,11 @@ function PhotoBoothApp() {
           const params = new URLSearchParams(window.location.search);
           const previewScreen = params.get("preview") as ScreenState | null;
           if (previewScreen === "result") {
-            const previewImg = params.get("image") || "/assets/styles/jack_o_lantern_sensei.jpg";
+            const previewImg = params.get("image") || "/assets/styles/jack_o_lantern_sensei.webp";
             setResultImage(previewImg);
             setScreen("result");
+          } else if (previewScreen === "finished") {
+            setScreen("finished");
           }
         }
       })
@@ -63,7 +66,7 @@ function PhotoBoothApp() {
     if (idleTimerRef.current) {
       clearTimeout(idleTimerRef.current);
     }
-    if (!config?.kiosk?.enableAutoReset || screen === "standby") {
+    if (!config?.kiosk?.enableAutoReset || screen === "standby" || screen === "finished") {
       return;
     }
     const timeoutMs = (config.kiosk.idleTimeoutSeconds || 90) * 1000;
@@ -178,6 +181,15 @@ function PhotoBoothApp() {
     setScreen("standby");
   };
 
+  const handleFinish = () => {
+    setCapturedPhoto(null);
+    setSelectedStyle(null);
+    setResultImage(null);
+    setErrorMessage(null);
+    setSafetyWarning(null);
+    setScreen("finished");
+  };
+
   if (!config) {
     return (
       <div className="flex h-screen w-screen items-center justify-center bg-[#090314] text-white">
@@ -246,10 +258,12 @@ function PhotoBoothApp() {
           config={config}
           resultImageUrl={resultImage}
           providerInfo={providerInfo}
-          onStartOver={handleStartOver}
+          onFinish={handleFinish}
         />
       )}
 
+      {screen === "finished" && <FinishedScreen />}
+
       {screen === "rate_limited" && (
         <RateLimitedScreen
           config={config}