Add option to customize or disable whimsical spinner text

Feature Request

The spinner/thinking indicator shows rotating whimsical words while Claude is working ("Pondering...", "Cogitating...", "Reticulating splines...", etc.). While intended to be playful, some users find this distracting or irritating and would prefer simple, professional text like "Working..." or "Planning next moves...".

Proposal

Add a setting (e.g. in settings.json) or a CLI flag to either:

1. Replace the whimsical spinner words with a single static message (e.g. "spinnerText": "Working...")
2. Disable whimsy entirely with a flag like --no-whimsy or a setting like "whimsySpinner": false

Example config

{
  "spinner": {
    "text": "Working..."
  }
}

Or simply:

{
  "whimsySpinner": false
}

This would be a small quality-of-life improvement for users who prefer a cleaner, less playful interface.