perf: compress hero image and defer page transition shutter

components/blocks/HeroVideo.tsx

@@ -80,10 +80,11 @@ export function HeroVideo(props: HeroVideoProps) {
       {/* Background color while video loads */}
       <div className="absolute inset-0 z-0 bg-neutral-dark" />
       
-      {/* ALWAYS render a native img as the LCP element to avoid Render Delay */}
       <img
         key={`img-${pathname}-${posterSrc}`}
         src={posterSrc}
+        srcSet={posterSrc.includes('-poster.webp') ? `${posterSrc.replace('-poster.webp', '-poster-mobile.webp')} 800w, ${posterSrc} 1920w` : undefined}
+        sizes={posterSrc.includes('-poster.webp') ? "(max-width: 768px) 800px, 1920px" : undefined}
         alt={posterAlt}
         className="absolute inset-0 w-full h-full object-cover z-[1] pointer-events-none"
         decoding="sync"