Drop tmux requirement from TUI

We currently have actions that are only implemented as tmux windows e.g. strategy editing, rebuilder attachment. It would be preferable to support cases where tmux isn't installed or active.

Start by locating the TUI actions currently implemented as tmux windows, especially strategy editing and rebuilder attachment. Determine how those actions behave when tmux is unavailable; done means the TUI supports these cases without requiring tmux to be installed or active.

Written by the indexing model from the issue text.