fix: fix user expiration date display and update issues

- Fix 1970 year display for unlimited validity users
- Resolve SQL error in user update endpoint
- Closes #625

app/Services/UserService.php

@@ -173,12 +173,11 @@ class UserService
         // 默认设置
         $user->remind_expire = admin_setting('default_remind_expire', 1);
         $user->remind_traffic = admin_setting('default_remind_traffic', 1);
+        $user->expired_at = 0;
 
         // 可选字段
         $this->setOptionalFields($user, $data);
 
-        $user->expired_at = 0;
-
         // 处理计划
         if (isset($data['plan_id'])) {
             $this->setPlanForUser($user, $data['plan_id'], $data['expired_at'] ?? null);