Allow customizing the thinking spinner text

The CLI shows random creative words while thinking (e.g. "Caramelizing (thinking)", "Simmering (thinking)"). It would be great to have a configuration option to customize or replace these with a simple static label like "THINKING".

This could be a setting in settings.json or .claude/config, e.g.:

{
  "thinkingSpinnerText": "THINKING"
}

Or even allow disabling the creative words entirely in favor of a static label.