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/zh.json

@@ -226,6 +226,8 @@
     "addIngredient": "添加食材",
     "ingredientNamePlaceholder": "食材",
     "ingredientQtyPlaceholder": "数量",
+    "ingredientCategoryLabel": "分类",
+    "ingredientCategoryDefault": "其他",
     "removeIngredient": "移除食材",
     "transferLabel": "将食材添加到购物清单",
     "transferNow": "立即添加",
@@ -596,4 +598,4 @@
     "unitMonth": "个月",
     "unitMonths": "个月"
   }
-}
+}