Feature Request: Show loading indicator in print mode

When running Claude in print mode (using the --print or -p flag), there is no visual feedback while Claude is thinking. This can make it seem like the program is hanging or has crashed, especially for long-running commands.

It would be great to have a loading indicator or spinner to show that Claude is processing the request. This would improve the user experience by providing feedback that the tool is working.

Something like this (this is generated using the gum spin CLI)

<img width="400" src="https://github.com/user-attachments/assets/52e020d8-ea59-419b-933c-e0e50e759942" />