feat: add demo site configuration flag

- Introduce `DemoSiteEnabled` variable in operation settings
- Provide a configurable flag to enable/disable demo site functionality

controller/misc.go

@@ -66,6 +66,7 @@ func GetStatus(c *gin.Context) {
 			"enable_online_topup":      setting.PayAddress != "" && setting.EpayId != "" && setting.EpayKey != "",
 			"mj_notify_enabled":        setting.MjNotifyEnabled,
 			"chats":                    setting.Chats,
+			"demo_site_enabled":        setting.DemoSiteEnabled,
 		},
 	})
 	return