Add shipping weight support for Snipcart delivery calculation

- Add weight field to product blueprint (in grams)
- Add data-item-shippable and data-item-weight attributes to product template
- Enable Snipcart to calculate shipping costs based on product weight

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

site/blueprints/pages/product.yml

@@ -33,6 +33,18 @@ tabs:
                   fr: Partagé entre les versions FR et EN
                 translate: false
                 width: 1/4
+              weight:
+                label:
+                  en: Weight (g)
+                  fr: Poids (g)
+                type: number
+                min: 0
+                default: 0
+                help:
+                  en: Weight in grams for shipping calculation
+                  fr: Poids en grammes pour le calcul de la livraison
+                translate: false
+                width: 1/4
               description:
                 label: Description panier
                 type: writer