Shopify Variants

Added

• Shopify Variants field: an ordered, optionally capped list of Shopify product variants.
• Shopify variant link type for Craft's native Link field, rendering a ?variant= storefront deep link.
• Variant search endpoint (shopify-variants/variants/search), paginated by product and matching on product title, variant title, and SKU.
• SelectedVariant::getImage(), which falls back to the product image for single-variant products, and getLabel(), which suppresses Shopify's Default Title placeholder.
• shopify-variants/check console command, asserting search, pagination, and GID round-trip against the synced catalog.