Stop a burn-in safely, even mid-run

Long multi-slot runs on shared instruments now stop the way an operator expects.

• Added a graceful stop on Ctrl-C, Ctrl-Break, SIGTERM and station stop: running phases are interrupted, the execution-scoped teardown (your power-off) runs, and every slot's run is queued as ABORTED with what it measured
• Added a second-signal escalation to force, ignored inside 3 s of the first so a reflex double Ctrl-C cannot cut a power-off in progress
• Fixed operator stops on multi-slot runs, where the shared plugs were released before the teardown could use them
• Fixed shared plug processes outliving the CLI and holding their instrument session after a crash or kill
• Fixed the operator screen showing idle after a reconnect hours into a run
• Changed phase deadlines to a monotonic clock, so a time sync no longer shortens a timeout

Closing the console window on Windows is best-effort inside the 5 s the OS grants; use Ctrl-C to stop a run, and an instrument-side watchdog for fixture safety.