Allow customizing the thinking spinner text

Question

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.:

```json
{
  "thinkingSpinnerText": "THINKING"
}
```

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