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/home/ProductCategories.tsx

@@ -43,7 +43,7 @@ export default function ProductCategories() {
 
   return (
     <Section className="bg-neutral-light py-0 md:py-0 lg:py-0 -mt-px">
-      <h2 className="sr-only">{t('title')}</h2>
+      {t('title') && <h2 className="sr-only">{t('title')}</h2>}
       <div className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-4">
         {categories.map((category, idx) => (
           <Link