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/layout.tsx

@@ -6,15 +6,14 @@ export const metadata: Metadata = {
   description:
     "上海健志空手道馆万圣节专属照相馆 (Shanghai Karate Club Halloween Photobooth) - 凝聚万圣气合，定格武道英姿！",
   icons: {
-    icon: "/assets/brand/shanghai_karate_logo.png",
+    icon: "/assets/brand/shanghai_karate_logo.webp",
   },
 };
 
 export const viewport: Viewport = {
   width: "device-width",
   initialScale: 1,
-  maximumScale: 1,
-  userScalable: false,
+  userScalable: true,
   viewportFit: "cover",
   themeColor: "#0b0714",
 };