docs: add ZPay referral recommendation to EasyPay section

docs/PAYMENT.md

@@ -96,6 +96,8 @@ Each provider type requires different credentials. Select the type when adding a
 
 Compatible with any payment service that implements the EasyPay protocol.
 
+> **EasyPay Recommendation**: [ZPay](https://z-pay.cn/?uid=23808) is recommended as an EasyPay provider (link contains the author's referral code — feel free to remove it). ZPay supports **individual users** (no business license required) with up to 10,000 CNY daily transactions; business-licensed accounts have no limit. Please evaluate the security, reliability, and compliance of any third-party payment provider on your own — this project does not endorse or guarantee any of them.
+
 | Parameter | Description | Required |
 |-----------|-------------|----------|
 | **Merchant ID (PID)** | EasyPay merchant ID | Yes |

docs/PAYMENT_CN.md

@@ -104,7 +104,7 @@ Sub2API 内置支付系统，支持用户自助充值，无需部署独立的支
 | **支付宝通道 ID** | 指定支付宝通道（可选） | 否 |
 | **微信通道 ID** | 指定微信通道（可选） | 否 |
 
-> **EasyPay 推荐**：[ZPay](https://z-pay.cn) 支持个人用户（无营业执照）每日 1 万元以内交易。支付渠道的安全性和合规性请自行鉴别。
+> **EasyPay 推荐**：个人推荐 [ZPay](https://z-pay.cn/?uid=23808) 作为 EasyPay 服务商（链接含作者邀请码，介意可去掉）。ZPay 支持**个人用户**（无营业执照）每日 1 万元以内交易；拥有营业执照则无限额。支付渠道的安全性、稳定性及合规性请自行鉴别，本项目不对任何第三方支付服务商做担保或背书。
 
 ### 支付宝官方