Add order history list endpoint

[Copilot]

Implements GET /api/orders endpoint to retrieve user's complete order history.

Changes

• OrderListResponse DTO: Summarizes orders with representative product (first item), total item count, and order metadata
• OrderRepository: Added findByUserIdOrderByCreatedAtDesc() for efficient order retrieval
• OrderConverter: Maps Order entities to list response with aggregated item counts
• OrderController: Exposes new GET endpoint at /api/orders

Response Structure

{
  "orderId": 123,
  "orderNumber": "ORD-20260204-a1b2c3d4",
  "orderStatus": "ORDER_RECEIVED",
  "representativeProductName": "Product Name",
  "representativeImageUrl": "https://...",
  "totalItemCount": 3,
  "totalAmount": 50000,
  "createdAt": "2026-02-04T10:36:00"
}

Orders are returned in descending chronological order (most recent first).

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[Feat]주문내역_초기주문 내역 화면</issue_title>
<issue_description>## 📌 Description

[Feat]주문내역_초기주문 내역 화면

✅ To-do

• 진행 예정
• 진행 완료

📒 기타</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Feat]주문내역_초기주문 내역 화면 #88

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.