feat: 新增退款凭证

openspec/changes/update-refund-voucher-multi-image/proposal.md

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+# Change: Update Refund Voucher Multi Image Behavior
+
+## Why
+
+退款管理需要更清晰地展示退款凭证，并支持一次退款记录关联多张凭证图片，便于财务核验。创建退款申请选择订单时也应只允许选择已支付订单，避免对未支付订单发起退款。
+
+## What Changes
+
+- 退款详情中直接展示退款凭证图片，点击图片后可放大预览。
+- 创建退款申请的订单号搜索/选择请求必须增加 `payment_status: 2` 条件。
+- 退款管理凭证上传支持多张图片，并将所有上传后的文件 key 以英文逗号拼接后放入 `refund_voucher_key` 参数。
+
+## Impact
+
+- Affected specs: `order-management`
+- Affected code:
+  - Refund detail voucher display and image preview behavior
+  - Create refund request order selector query params
+  - Refund management voucher upload component and submit payload
+- Breaking changes: Refund voucher payload field for this flow remains `refund_voucher_key` and supports one or more uploaded image keys separated by English commas.