fix(port-forward): clear port file instead of removing it

- Prevent port forwarding loop crash when trying to delete a directly bind mounted file
- See https://github.com/qdm12/gluetun/issues/2942#issuecomment-3468510402

internal/portforward/service/stop.go

@@ -3,7 +3,6 @@ package service
 import (
 	"context"
 	"fmt"
-	"os"
 	"time"
 )
 
@@ -61,10 +60,10 @@ func (s *Service) cleanup() (err error) {
 	s.ports = nil
 
 	filepath := s.settings.Filepath
-	s.logger.Info("removing port file " + filepath)
-	err = os.Remove(filepath)
+	s.logger.Info("clearing port file " + filepath)
+	err = s.writePortForwardedFile(nil)
 	if err != nil {
-		return fmt.Errorf("removing port file: %w", err)
+		return fmt.Errorf("clearing port file: %w", err)
 	}
 
 	return nil