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/screens/StandbyScreen.tsx

@@ -29,7 +29,7 @@ export const StandbyScreen: React.FC<StandbyScreenProps> = ({
           <h2 className={`text-2xl sm:text-3xl md:text-4xl font-black text-amber-100 tracking-wider drop-shadow-[0_4px_12px_rgba(0,0,0,0.95)] ${language === 'en' ? 'font-cinzel' : 'font-dojo'}`}>
             {t(labels.welcomeTitle)}
           </h2>
-          <p className="text-amber-400/95 font-semibold text-[11px] sm:text-xs tracking-widest uppercase drop-shadow-[0_2px_4px_rgba(0,0,0,0.9)]">
+          <p className="text-amber-400/95 font-semibold text-xs sm:text-xs tracking-widest uppercase drop-shadow-[0_2px_4px_rgba(0,0,0,0.9)]">
             {t(labels.welcomeSubtitle)}
           </p>
         </div>
@@ -51,7 +51,7 @@ export const StandbyScreen: React.FC<StandbyScreenProps> = ({
       <div className="z-10 w-full flex flex-col items-center pb-1">
         <button
           onClick={onStart}
-          className="w-full max-w-[210px] sm:max-w-[240px] py-2 sm:py-2.5 px-4 game-btn-gold font-extrabold text-xs sm:text-sm tracking-wider flex items-center justify-center space-x-2 text-center select-none uppercase font-cinzel shadow-lg"
+          className="w-full max-w-[210px] sm:max-w-[240px] py-2 sm:py-2.5 px-4 game-btn-gold font-extrabold text-sm tracking-wider flex items-center justify-center space-x-2 text-center select-none uppercase font-cinzel shadow-lg"
         >
           <span>{t(labels.welcomeCta)}</span>
         </button>