vercel/commerce ? reverse-engineered prompt

Build me a fast modern online store using this Next.js Commerce template, with Shopify as the backend. I want it to feel like a real production storefront, not just a demo, so customers should be able to browse products and collections, search, open product pages, add items to a cart, and continue to checkout through Shopify.

Please wire up whatever environment settings are needed from the example env file, make sure it runs locally, and keep it ready to deploy on Vercel. Use the existing structure instead of reinventing everything, and keep the Shopify specific parts where they belong so the rest of the app stays clean.

If there are any missing setup details, check the current Vercel and Shopify docs online and fill in the gaps. I would also like sensible defaults for branding using the company and site name env values, and a polished storefront feel with good loading performance and responsive behavior on mobile and desktop.