feat: per-ingredient category selection for shopping list transfer (closes #33)

When adding ingredients in the meal editor, each ingredient now has a
category dropdown. Categories are stored on the ingredient and applied
automatically when transferring to the shopping list, so items appear
pre-grouped by category without manual re-sorting.

public/locales/es.json

@@ -226,6 +226,8 @@
     "addIngredient": "Añadir ingrediente",
     "ingredientNamePlaceholder": "Ingrediente",
     "ingredientQtyPlaceholder": "Cantidad",
+    "ingredientCategoryLabel": "Categoría",
+    "ingredientCategoryDefault": "Varios",
     "removeIngredient": "Eliminar ingrediente",
     "transferLabel": "Transferir ingredientes a la lista de compras",
     "transferNow": "Transferir ahora",
@@ -596,4 +598,4 @@
     "unitMonth": "mes",
     "unitMonths": "meses"
   }
-}
+}