Feature request: kill all windows

Sometimes a session gets stuck or terminates, but blink is no longer responsive in that session (but it is possible to create a new prompt and issue commands from it). It would be nice to be able to Command-T to get a new prompt, and issue a `kill` command to kill a window or the entire blink session. Right now I have 2 dead sessions and no way to get rid of them.

No file, test, or entry point is named in the issue. Start by reproducing the stuck-session state in Blink on iOS or iPadOS and trace how Command-T creates a prompt and how existing windows or sessions receive commands. Done means a kill command can remove either the selected window or the entire Blink session, including dead sessions.

Written by the indexing model from the issue text.