perf(booth): optimize assets and result flow

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

components/MascotGuide.tsx

@@ -19,10 +19,10 @@ interface MascotGuideProps {
 }
 
 const POSE_IMAGES: Record<MascotPose, string> = {
-  bow: "/assets/theme/mascot_bow.png",
-  punch: "/assets/theme/mascot_punch.png",
-  kick: "/assets/theme/mascot_kick.png",
-  zen: "/assets/theme/mascot_zen.png",
+  bow: "/assets/theme/mascot_bow.webp",
+  punch: "/assets/theme/mascot_punch.webp",
+  kick: "/assets/theme/mascot_kick.webp",
+  zen: "/assets/theme/mascot_zen.webp",
 };
 
 export const MascotGuide: React.FC<MascotGuideProps> = ({
@@ -94,7 +94,7 @@ export const MascotGuide: React.FC<MascotGuideProps> = ({
             )}
 
             <p
-              className={`text-amber-100 font-extrabold text-[12px] sm:text-[14px] leading-snug drop-shadow-[0_1px_2px_rgba(0,0,0,0.8)] ${
+              className={`text-amber-100 font-extrabold text-sm leading-snug drop-shadow-[0_1px_2px_rgba(0,0,0,0.8)] ${
                 language === "en" ? "font-cinzel" : "font-dojo"
               }`}
             >