fix: rsa2_sign后备逻辑改为from_pkcs8_der(支持裸Base64私钥)

src/handlers/payment.rs

@@ -96,9 +96,8 @@ fn rsa2_sign(content: &str, private_key_pem: &str) -> Result<String, String> {
                 private_key_pem,
             )
             .map_err(|e| format!("Base64 解码失败: {}", e))?;
-            let pem_str = String::from_utf8(decoded)
-                .map_err(|e| format!("PEM 字符串格式错误: {}", e))?;
-            RsaPrivateKey::from_pkcs8_pem(&pem_str)
+            // 支付宝密钥工具生成的 Base64 解码后是 PKCS#8 DER，不是 PEM 文本
+            RsaPrivateKey::from_pkcs8_der(&decoded)
                 .map_err(|e| format!("私钥解析失败: {}", e))?
         }
     };