chore: achieve 100/100 pagespeed and html validation

- fix html validation errors in blog mdx (empty headings)
- fix backstopjs esm compatibility and missing reference images
- optimize product data structure and next.config.mjs
- finalize accessibility and seo improvements

components/Footer.tsx

@@ -19,6 +19,7 @@ export default function Footer() {
       <div className="absolute top-0 left-0 w-full h-px bg-gradient-to-r from-transparent via-white/20 to-transparent" />
 
       <Container>
+        <h2 className="sr-only">Footer Navigation</h2>
         <div className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-12 gap-16 mb-20">
           {/* Brand Column */}
           <div className="lg:col-span-4 space-y-8">