Add i18n support and cart total to Shopify integration

Implement multilingual support for shop interface and add total calculation to cart drawer:
- Add FR/EN translations for all shop-related texts (cart, checkout, stock status)
- Update templates and JavaScript to use translation system
- Add cart total calculation with formatted currency display
- Refactor cart drawer styles to SASS with improved button styling (black borders on +/-)
- Fix English product content (replace JSON with proper HTML)
- Extract cart drawer to separate snippet for better organization

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

assets/js/product-add-to-cart.js

@@ -21,6 +21,16 @@
   const variantId = addToCartBtn.dataset.variantId;
   const stockDisplay = document.querySelector('[data-product-stock]');
 
+  // Get translated texts
+  const texts = {
+    add: addToCartBtn.dataset.textAdd || 'Add to cart',
+    adding: addToCartBtn.dataset.textAdding || 'Adding...',
+    added: addToCartBtn.dataset.textAdded || 'Added! ✓',
+    error: addToCartBtn.dataset.textError || 'Error - Try again',
+    outOfStock: addToCartBtn.dataset.textOutOfStock || 'Out of stock',
+    inStock: addToCartBtn.dataset.textInStock || 'In stock'
+  };
+
   // Load product data to check availability
   async function loadProductData() {
     try {
@@ -49,16 +59,16 @@
       // Update button based on availability
       if (!variant.availableForSale) {
         addToCartBtn.disabled = true;
-        addToCartBtn.textContent = 'Rupture de stock';
+        addToCartBtn.textContent = texts.outOfStock;
         addToCartBtn.classList.add('out-of-stock');
         if (stockDisplay) {
-          stockDisplay.textContent = 'Rupture de stock';
+          stockDisplay.textContent = texts.outOfStock;
           stockDisplay.classList.add('out-of-stock');
         }
       } else {
         // Show in stock
         if (stockDisplay) {
-          stockDisplay.textContent = 'En stock';
+          stockDisplay.textContent = texts.inStock;
           stockDisplay.classList.add('in-stock');
         }
       }
@@ -78,14 +88,14 @@
     // Disable button during request
     addToCartBtn.disabled = true;
     const originalText = addToCartBtn.textContent;
-    addToCartBtn.textContent = 'Ajout en cours...';
+    addToCartBtn.textContent = texts.adding;
 
     try {
       const variantId = this.dataset.variantId;
       const cartResult = await cart.addToCart(variantId, 1);
 
       // Show success feedback
-      addToCartBtn.textContent = 'Ajouté ! ✓';
+      addToCartBtn.textContent = texts.added;
       addToCartBtn.classList.add('success');
 
       // Dispatch event to open cart drawer
@@ -104,7 +114,7 @@
       console.error('Error adding to cart:', error);
 
       // Show error feedback
-      addToCartBtn.textContent = 'Erreur - Réessayer';
+      addToCartBtn.textContent = texts.error;
       addToCartBtn.classList.add('error');
 
       // Re-enable button after delay