Windows: an unsupervised gap run can leave child processes running (no process tree kill) #74

Found in the review of #58 (F4e). An unsupervised win32 run, the one without a supervisor (Windows has no process groups), is exempt from "no process outlives the CLI": a Vitest worker or a browser driver a test starts can outlive the CLI there. This predates #58.

Proposed fix: kill the process tree on win32 with Job Objects (a job with kill-on-close, assigned at start) or with taskkill /T /F /PID <pid> on stop and at exit. Acceptance: a hooked or real stop leaves no node.exe child running under the run's PID tree.