fix: use static male business avatar instead of DiceBear API

Single default_avatar.png for all new registrations - clean, professional male silhouette.

application/api/controller/User.php

@@ -187,9 +187,8 @@ class User extends Api
         }
 //        }
         $extend['pay_pwd'] = strtoupper(md5(strtoupper(md5($pwd2.'skund'))));
-        // 生成随机虚拟头像 (DiceBear avataaars 商务风格，URL需<255字符)
+        // 默认男性商务头像（静态图片）
-        $avatarSeed = substr(md5(uniqid(mt_rand(), true)), 0, 8);
+        $extend['avatar'] = '/uploads/default_avatar.png';
-        $extend['avatar'] = 'https://api.dicebear.com/9.x/avataaars/png?seed=' . $avatarSeed;
         $extend['referral_code'] = $this->create_invite_code();    //推荐码
         //注册钱包eth
         $ret = $this->auth->register($username, $password, $email, $mobile, $extend);