fix: disable captcha verification by default

- Change selectCaptchaOnOff() default from true to false
- Compatible with new frontend (ruoyi-ui-next) which has no captcha input
- Existing explicit config still takes effect

ruoyi-system/src/main/java/com/ruoyi/system/service/impl/SysConfigServiceImpl.java

@@ -95,7 +95,8 @@ public class SysConfigServiceImpl implements ISysConfigService
         String captchaOnOff = selectConfigByKey("sys.account.captchaOnOff");
         if (StringUtils.isEmpty(captchaOnOff))
         {
-            return true;
+            // 默认关闭验证码，兼容无验证码输入框的前端
+            return false;
         }
         return Convert.toBool(captchaOnOff);
     }