refactor(config): improve config file handling and error messages

- Replace manual address formatting with net.JoinHostPort in tcpClient
- Simplify debug/error messages in IsInstanceRunning by removing redundant output
- Fix incorrect map reference for RunUser in CreateInstanceHandler
- Extract config file creation logic into handleConfigFileCreate
- Add auth_token to response data in GetInstanceInfoHandler
- Remove redundant AuthToken field from InstanceInfo struct

watchdog/tcpClient.go

@@ -42,7 +42,7 @@ func tcpConnect(ipaddr string, port int) error {
 		return fmt.Errorf("already connected")
 	}
 
-	address := fmt.Sprintf("%s:%d", ipaddr, port)
+	address := net.JoinHostPort(ipaddr, fmt.Sprintf("%d", port))
 	conn, err := net.DialTimeout("tcp", address, 3*time.Second)
 	if err != nil {
 		return fmt.Errorf("failed to connect to %s: %v", address, err)