Add comprehensive SEO optimization

Implement complete SEO setup for virtual product pages with:
- Meta tags (title, description, canonical, hreflang)
- Open Graph protocol for social sharing
- Twitter Card tags
- Schema.org structured data (JSON-LD) for products
- XML sitemap including virtual pages
- Dynamic meta tag updates via JavaScript

Changes:
- Create SEO snippet with all meta tags
- Add structured data snippet for products
- Generate sitemap.xml with products and hreflang
- Update meta tags dynamically when Shopify data loads
- Remove noindex/nofollow (was blocking all indexing)
- Add product-specific OG tags (price, availability)

All pages now properly indexed with correct multilingual setup.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

site/templates/product.php

@@ -48,4 +48,5 @@ snippet('header', ['title' => $page->title(), 'template' => 'shop']);
     </section>
 </main>
 
+<?php snippet('structured-data-product') ?>
 <?php snippet('footer', ['scripts' => ['product']]) ?>