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/css/components/_shopify-buy-button.scss

@@ -0,0 +1,68 @@
+.product-purchase {
+  margin-top: 2rem;
+}
+
+.product-stock-info {
+  margin-bottom: 1rem;
+}
+
+.stock-status {
+  font-size: 0.9rem;
+  font-weight: 600;
+  margin: 0;
+}
+
+.stock-status.in-stock {
+  color: #00cc00;
+}
+
+.stock-status.low-stock {
+  color: #ff9900;
+}
+
+.stock-status.out-of-stock {
+  color: #ff3333;
+}
+
+.btn-add-to-cart {
+  font-family: "Open Sans", sans-serif;
+  font-weight: bold;
+  font-size: 1rem;
+  color: #000000;
+  background-color: #00ff00;
+  border: none;
+  border-radius: 40px;
+  padding: 12px 34px;
+  cursor: pointer;
+  transition: background-color 0.3s ease;
+  width: 100%;
+  max-width: 300px;
+}
+
+.btn-add-to-cart:hover:not(:disabled) {
+  background-color: #00e600;
+}
+
+.btn-add-to-cart:focus {
+  outline: 2px solid #00e600;
+  outline-offset: 2px;
+}
+
+.btn-add-to-cart:disabled {
+  opacity: 0.6;
+  cursor: not-allowed;
+}
+
+.btn-add-to-cart.success {
+  background-color: #00cc00;
+}
+
+.btn-add-to-cart.error {
+  background-color: #ff3333;
+  color: #ffffff;
+}
+
+.btn-add-to-cart.out-of-stock {
+  background-color: #cccccc;
+  color: #666666;
+}