[FEATURE] Improve visual feedback when a model is thinking

[edenreich]

Summary

The CLI is not showing anything when the model is "thinking".

The ideal behavior should be a greyed out text to mark it as non-important shown just in a collapsed box, allowing the user to expand it if they wish.

Acceptance Criteria

• Thinking content generation is shown to the user in a collapsed box with just the first sentence
• There is a configurable keybinding to expand the thinking
• It's tested
• It's documented