Allow copying text from the command menu (e.g. /help, /models output)

Summary

Content shown by command-menu commands (e.g. /help, /models) can't be copied. It would be very useful to select and copy text out of the command menu so it can be pasted elsewhere.

Motivation

A concrete case: when I run /models, I want to copy a model name to use as a reference — for example when asking the system to spawn an agent using a specific model. Today I have to retype the model ID by hand, which is error-prone (a wrong/stale ID currently fails with 404 no provider is configured).

Proposed behavior

• Allow selecting and copying text rendered by command-menu commands like /help and /models.
• Ideally support copying an individual item (e.g. a single model name/ID) as well as the full block.

Notes

Applies to the mecatui command menu / slash-command output rendering.