Make GUI kill processes forcibly after a short timeout

Currently GUI can linger for quite a while in some cases, and keep sockets bound etc.

"Close" event should probably wait for nice shutdown for a few seconds, and then just kill everything if necessary.

Master doesn't write to disk at all, and client just rehashes stuff on startup, so corrupting files or such shouldn't be a problem.

Locate the GUI "Close" event and trace how the master and client processes shut down, including where sockets remain bound. Confirm the existing graceful-shutdown path, then verify that closing waits briefly before forcibly terminating any processes that remain; done means the GUI exits promptly without lingering processes or bound sockets.

Written by the indexing model from the issue text.