Convert and compress all images to WebP format

Images account for 577 KiB of avoidable data transfer on mobile and 746 KiB on desktop, directly causing the 17.2s mobile LCP and degrading user experience for customers on slower connections.

In Shopify theme settings, ensure all section images use Shopify's built-in image optimization. Add ?format=webp&width={display_width} to image URLs in theme Liquid files. For the hero image, set a maximum width of 1440px.