watch: handle SIGHUP in watcher interrupt path

[SergioChan]

Summary

• include syscall.SIGHUP in the watcher interrupt signal handler
• watcher mode now exits/restarts on SIGHUP just like SIGINT/SIGTERM

Testing

• Unable to run go test ./... locally in this environment because the repository requests Go 1.25 toolchain and automatic toolchain download is unavailable here (toolchain not available).
• Change is a single signal list update in closeOnInterrupt, with no behavioral impact outside watch-mode signal handling.

Related

• Fixes Watcher interrupt on SIGHUP #2642

[trulede]

What would happen if both SIGTERM and SIGHUP are received in quick succession? Is it going to restart the watcher, or exit Task.

Possibly call signal.Stop(ch) before w.Close(),