feat: 新增数据库迁移，为 tb_agent_recharge_record 添加 payment_voucher_key 列

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

migrations/000128_add_payment_voucher_key_to_agent_recharge_record.down.sql

@@ -0,0 +1,2 @@
+ALTER TABLE tb_agent_recharge_record
+    DROP COLUMN IF EXISTS payment_voucher_key;

migrations/000128_add_payment_voucher_key_to_agent_recharge_record.up.sql

@@ -0,0 +1,6 @@
+-- 为 tb_agent_recharge_record 表添加支付凭证字段
+-- 允许 NULL，兼容历史数据；新接口在 Service 层对 offline 支付方式强制非空校验
+ALTER TABLE tb_agent_recharge_record
+    ADD COLUMN IF NOT EXISTS payment_voucher_key VARCHAR(500);
+
+COMMENT ON COLUMN tb_agent_recharge_record.payment_voucher_key IS '支付凭证对象存储Key（线下支付时必填，微信支付时为空）';