Recovers the manual click on the details accordion: with #14968's new
SECTION_DEFAULTS (thinking/tools start `expanded`), every panel render
was OR-ing the local open toggle against `visible.X === 'expanded'`.
That pinned `open=true` for the default-expanded sections, so clicking
the chevron flipped the local state but the panel never collapsed.
Local toggle is now the sole source of truth at render time; the
useState init still seeds from the resolved visibility (so first paint
is correct) and the existing useEffect still re-syncs when the user
mutates visibility at runtime via `/details`.
Same OR-lock cleared inside SubagentAccordion (`showChildren ||
openX`) — pre-existing but the same shape, so expand-all on the
spawn tree no longer makes inner sections un-collapsible either.