function setAssistantWindowBorder() {
  const validBorders = ['none', 'prominent', 'minimal', 'color-shift'];

  const windowBorderValue = validBorders.includes(assistantConfig['windowBorder'])
    ? assistantConfig['windowBorder']
    : 'none';

  document
    .querySelector('#master-bg')
    .setAttribute('data-border', windowBorderValue);
}
Sets the window border based on config.