[Feature]: 兑换码

[qingchunnh]

Affected area

Backend / API

Problem or use case

以我个人来说我自己和我朋友使用的话可以方便很多，不需要配置支付也不用等他们注册后后台修改余额什么的

Proposed behavior

允许创建兑换码，最好可以手动生成也可以随机生成，可以修改兑换次数，比如创建一个叫2026的兑换码设为无限次，这样所有注册的用户都可以使用2026来兑换，又或者是直接随机生成的一次性兑换码

Alternatives considered

No response

Compatibility, deployment, or migration impact

No response

Documentation or API contract impact

No response

Pre-submit checklist

• I searched existing issues and pull requests.
• This request is focused on one feature or improvement.
• I described user-facing, API, configuration, or deployment impact where relevant.