Implement order cancellation endpoint

[Copilot]

Adds order cancellation functionality allowing users to cancel orders in ORDER_RECEIVED status with automatic point refunds.

Changes

API

• DELETE /api/orders/{orderId} - Cancel order with validation and point refund
• Returns OrderCancelResponse with cancellation details

Data Model

• Order.usedPoints - Track points used during purchase for refund calculation
• Order.cancel() - Encapsulates status transition and timestamp setting
• User.increasePoints() - Handle point refunds

Business Logic

• Validates order ownership and status (only ORDER_RECEIVED cancellable)
• Refunds usedPoints to user balance
• Sets orderStatus = CANCELED and canceledAt timestamp

Error Codes

• ORDER_ALREADY_CANCELED - Duplicate cancellation attempt
• ORDER_CANNOT_BE_CANCELED - Invalid status for cancellation

Example

// Cancel an order
DELETE /api/orders/123

// Response
{
  "orderId": 123,
  "orderNumber": "ORD-20260206-a1b2c3d4",
  "orderStatus": "취소",
  "refundedPoints": 5000,
  "canceledAt": "2026-02-06T10:30:00"
}

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Feat] 주문 취소 화면</issue_title>
<issue_description>## 📌 Description

[Feat] 주문 취소 화면

✅ To-do

• 진행 예정
• 진행 완료

📒 기타</issue_description>

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

• Fixes [Feat] 주문 취소 화면 #91

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