feat: 后台线下支付订单强制上传支付凭证

在后台创建订单接口中新增 payment_voucher_key 字段，线下支付方式
下该字段为必填，存储对象存储 file_key，便于后续追溯与审计。

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

migrations/000109_add_payment_voucher_to_order.down.sql

@@ -0,0 +1 @@
+ALTER TABLE tb_order DROP COLUMN IF EXISTS payment_voucher_key;

migrations/000109_add_payment_voucher_to_order.up.sql

@@ -0,0 +1,2 @@
+ALTER TABLE tb_order ADD COLUMN IF NOT EXISTS payment_voucher_key VARCHAR(500);
+COMMENT ON COLUMN tb_order.payment_voucher_key IS '线下支付凭证对象存储 file_key（仅线下支付订单必填）';