api.sx gains sessions(Subject) (enumerate a subject's live sessions) and
logout_all(Subject) ("log out everywhere") — revokes and deregisters every
session the subject holds, auditing a logout per session, leaving other
subjects' sessions untouched. Builds on registry.sessions_for. New
tests/session_mgmt.sx. 193/193.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
