feat(shop): wire storefront buy path to server cart

Connect product options/add-cart, server cart checkout payloads,
favorite/rebuy/receipt REST, and order-center actions without
localStorage dual-read or hardcoded cart/orders URL hacks.

templates/pages/page-product.php

@@ -46,6 +46,10 @@ $author = $author_id > 0 ? get_userdata($author_id) : null;
             data-aksrt-product-page
             data-product-id="<?php echo esc_attr((string) $product_id); ?>"
             data-options='<?php echo esc_attr(wp_json_encode($options, JSON_UNESCAPED_UNICODE)); ?>'
+            data-base-price="<?php echo esc_attr((string) (($product['start_price'] ?? 0) > 0 ? $product['start_price'] : ($product['price'] ?? 0))); ?>"
+            data-base-stock="<?php echo esc_attr((string) ($product['stock'] ?? 0)); ?>"
+            data-pay-modo="<?php echo esc_attr((string) $pay_modo); ?>"
+            data-price-range="<?php echo !empty($price_range) && (($price_range['min'] ?? 0) !== ($price_range['max'] ?? 0)) ? '1' : '0'; ?>"
         >
             <div class="aksrt-product-page__layout">
                 <!-- Gallery -->