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>

content/1_tshirt-index-01/product.en.txt

@@ -10,26 +10,7 @@ Description: <p>T-shirt de soutien à Index, 100% coton</p>
 
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-Details:
-
-[
-  {
-    "content": {
-      "text": "<p>100% cotton</p>"
-    },
-    "id": "detail1",
-    "isHidden": false,
-    "type": "text"
-  },
-  {
-    "content": {
-      "text": "<p>Lorem ipsum dolor sit amet</p>"
-    },
-    "id": "detail2",
-    "isHidden": false,
-    "type": "text"
-  }
-]
+Details: <p>Organic cotton t-shirt with screen printing.<br>Print on the front: "INDEX" logo, 10 cm wide.</p><ul><li><p>100% organic cotton</p></li><li><p>Weight: 180 g/m²</p></li><li><p>Single jersey with very soft feel</p></li><li><p>Excellent durability over time</p></li><li><p>Internal neckband</p></li><li><p>Double stitching on sleeves and bottom hem</p></li></ul><p>Shipping only via Mondial Relay to France, Belgium and Switzerland.</p>
 
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