Round 23: Flagship homepage template — DTC polish + B2B function

New first-party `homepage-flagship` builder template, recommended for trade merchants. 9 sections: announcement bar, hero with trade CTA, 4-icon value-prop strip, featured categories (category-first beats product-first for SMB), bestsellers carousel, editorial split, review highlights, new arrivals, payment trust badges. Sits above homepage-commerce in the picker as the default for new tenants.