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>

tests/routes/items.test.ts

@@ -118,4 +118,30 @@ describe("Item Routes", () => {
 		const res = await app.request("/api/items/9999");
 		expect(res.status).toBe(404);
 	});
+
+	it("POST /api/items/:id/duplicate returns 201 with the copy", async () => {
+		const createRes = await app.request("/api/items", {
+			method: "POST",
+			headers: { "Content-Type": "application/json" },
+			body: JSON.stringify({ name: "Tent", categoryId: 1, weightGrams: 1200 }),
+		});
+		const created = await createRes.json();
+
+		const res = await app.request(`/api/items/${created.id}/duplicate`, {
+			method: "POST",
+		});
+
+		expect(res.status).toBe(201);
+		const body = await res.json();
+		expect(body.name).toBe("Tent (copy)");
+		expect(body.weightGrams).toBe(1200);
+		expect(body.id).not.toBe(created.id);
+	});
+
+	it("POST /api/items/999/duplicate returns 404", async () => {
+		const res = await app.request("/api/items/999/duplicate", {
+			method: "POST",
+		});
+		expect(res.status).toBe(404);
+	});
 });

tests/services/item.service.test.ts

@@ -2,6 +2,7 @@ import { beforeEach, describe, expect, it } from "bun:test";
 import {
 	createItem,
 	deleteItem,
+	duplicateItem,
 	getAllItems,
 	getItemById,
 	updateItem,
@@ -98,6 +99,41 @@ describe("Item Service", () => {
 		});
 	});
 
+	describe("duplicateItem", () => {
+		it("creates a copy with '(copy)' suffix in name", () => {
+			const original = createItem(db, {
+				name: "Tent",
+				weightGrams: 1200,
+				priceCents: 35000,
+				categoryId: 1,
+				notes: "Ultralight",
+				productUrl: "https://example.com/tent",
+			});
+
+			const copy = duplicateItem(db, original?.id);
+
+			expect(copy).toBeDefined();
+			expect(copy?.name).toBe("Tent (copy)");
+			expect(copy?.weightGrams).toBe(1200);
+			expect(copy?.priceCents).toBe(35000);
+			expect(copy?.categoryId).toBe(1);
+			expect(copy?.notes).toBe("Ultralight");
+			expect(copy?.productUrl).toBe("https://example.com/tent");
+		});
+
+		it("copy has a different ID from the original", () => {
+			const original = createItem(db, { name: "Helmet", categoryId: 1 });
+			const copy = duplicateItem(db, original?.id);
+
+			expect(copy?.id).not.toBe(original?.id);
+		});
+
+		it("returns null for non-existent item", () => {
+			const result = duplicateItem(db, 9999);
+			expect(result).toBeNull();
+		});
+	});
+
 	describe("deleteItem", () => {
 		it("removes item from DB, returns deleted item", () => {
 			const created = createItem(db, {