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/server/services/item.service.ts

@@ -104,6 +104,28 @@ export function updateItem(
 		.get();
 }
 
+export function duplicateItem(db: Db = prodDb, id: number) {
+	const source = db.select().from(items).where(eq(items.id, id)).get();
+
+	if (!source) return null;
+
+	return db
+		.insert(items)
+		.values({
+			name: `${source.name} (copy)`,
+			weightGrams: source.weightGrams,
+			priceCents: source.priceCents,
+			categoryId: source.categoryId,
+			notes: source.notes,
+			productUrl: source.productUrl,
+			imageFilename: source.imageFilename,
+			imageSourceUrl: source.imageSourceUrl,
+			quantity: source.quantity,
+		})
+		.returning()
+		.get();
+}
+
 export function deleteItem(db: Db = prodDb, id: number) {
 	// Get item first (for image cleanup info)
 	const item = db.select().from(items).where(eq(items.id, id)).get();