Get one Wendy's menu item's (or combo's) detail

Returns one item's full detail. A simple item (is_combo false) returns its description, base price, calories, every size/weight variant (e.g. Small/Medium/Large fries, each with its own price and calories, with is_default marking the one Wendy's own page pre-selects), and every modifier component -- default (comes with the item), extra (a paid add-on) and required (the caller must pick one option from a named group, e.g. a salad's dressing) -- each with its own ingredient description and allergen list, since Wendy's publishes allergens per-component rather than as one whole-item field. The top-level allergens field is the union across default components and each required group's default-selected option only. A combo (is_combo true) instead returns combo_slots: its entree/side/drink composition and every product each slot can be built from, since a combo's own price and calories vary by what is chosen. A combo slot's product ids are the same items sold standalone in their own categories -- call this endpoint again on one of those for its own full component/allergen detail. Category and item slugs come from GET /wendys/categories and GET /wendys/menu.