feat(cloud): Allow teardown without collection

[fuyu0425]

Summary

• add cloud teardown --skip-collect so teardown can reclaim the fleet without collecting artifacts or logs
• add an interactive s / skip option when teardown encounters an existing local destination, alongside the existing timestamp path
• add CLI/unit coverage and update the cloud teardown docs/design notes

Testing

• scripts/ci-tests/run-local.sh checks

Notes

• --timestamp and --skip-collect are mutually exclusive for teardown
• default teardown behavior remains collect-first unless skip is explicitly requested