teardown-stage2.sh stops every Stage 2 run (daemon + docs + sandbox), kills any
orphaned sandbox dev server on :4311 the onboarding-tester left behind, and stops
the regtest BTCPay docker stack + volumes (--keep-btcpay to leave it up). README
documents it as the always-run cleanup step, and adds a harvest note: on a clean
run, check whether the existing public docs already cover the success story before
adding anything.
Grant