--no-team is a one-shot teardown, so every later bare ./setup (including the
ones /gstack-upgrade runs) re-registered the timeline Stop hook with no way
to say 'never'. New gate mirrors the plan_tune_hooks pattern: flag
(--timeline-stop-hook/--no-timeline-stop-hook) > env
(GSTACK_TIMELINE_STOP_HOOK) > saved config (timeline_stop_hook) > default
yes. An explicit flag persists to config so the decision survives upgrades;
an explicit 'no' also removes a live registration (reconciliation), so the
opt-out works against installs registered by an older setup. --no-team
semantics unchanged (NO_TEAM_MODE is never initialized from config). Full
gstack-config surface: DEFAULTS entry, header docs, list/defaults
enumeration, warn-and-default validation.
Fixes#2677
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
