feat: add item duplication with copy-and-edit workflow

Adds POST /api/items/:id/duplicate endpoint, useDuplicateItem hook, and a
Duplicate button on ItemCard (collection view only) that opens the new item
for editing immediately after creation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/client/components/ItemCard.tsx

@@ -1,4 +1,5 @@
 import { useFormatters } from "../hooks/useFormatters";
+import { useDuplicateItem } from "../hooks/useItems";
 import { LucideIcon } from "../lib/iconData";
 import { useUIStore } from "../stores/uiStore";
 import { ClassificationBadge } from "./ClassificationBadge";
@@ -35,6 +36,7 @@ export function ItemCard({
 	const { weight, price } = useFormatters();
 	const openEditPanel = useUIStore((s) => s.openEditPanel);
 	const openExternalLink = useUIStore((s) => s.openExternalLink);
+	const duplicateItem = useDuplicateItem();
 
 	return (
 		<button
@@ -42,6 +44,46 @@ export function ItemCard({
 			onClick={() => openEditPanel(id)}
 			className="relative w-full text-left bg-white rounded-xl border border-gray-100 hover:border-gray-200 hover:shadow-sm transition-all overflow-hidden group"
 		>
+			{!onRemove && (
+				<span
+					role="button"
+					tabIndex={0}
+					onClick={(e) => {
+						e.stopPropagation();
+						duplicateItem.mutate(id, {
+							onSuccess: (newItem) => {
+								openEditPanel(newItem.id);
+							},
+						});
+					}}
+					onKeyDown={(e) => {
+						if (e.key === "Enter" || e.key === " ") {
+							e.stopPropagation();
+							duplicateItem.mutate(id, {
+								onSuccess: (newItem) => {
+									openEditPanel(newItem.id);
+								},
+							});
+						}
+					}}
+					className={`absolute top-2 ${productUrl ? "right-10" : "right-2"} z-10 w-6 h-6 flex items-center justify-center rounded-full bg-gray-100/80 text-gray-400 hover:bg-blue-100 hover:text-blue-500 opacity-0 group-hover:opacity-100 transition-all cursor-pointer`}
+					title="Duplicate item"
+				>
+					<svg
+						className="w-3.5 h-3.5"
+						fill="none"
+						stroke="currentColor"
+						viewBox="0 0 24 24"
+					>
+						<path
+							strokeLinecap="round"
+							strokeLinejoin="round"
+							strokeWidth={2}
+							d="M8 16H6a2 2 0 01-2-2V6a2 2 0 012-2h8a2 2 0 012 2v2m-6 12h8a2 2 0 002-2v-8a2 2 0 00-2-2h-8a2 2 0 00-2 2v8a2 2 0 002 2z"
+						/>
+					</svg>
+				</span>
+			)}
 			{productUrl && (
 				<span
 					role="button"