Two changes from mara's review:
1. drop the manager special-case. Both M0V3 affordances now apply
regardless of whether the manager is in the selection; backend
topology::set_parent refuses the manager move and the failure
surfaces in the bulk-action error roll-up. Matches the #443 ST0P
policy of 'don't pre-gate manager actions, let the backend speak'.
2. enable the M0V3 → <pick> picker for multi-select. Was single-agent
only in v1. Picker now omits every selected agent itself plus the
union of every selected agent's descendants (cycle-safe across the
whole batch); on submit POSTs once per selected agent sequentially,
same shape as the existing bulk-button loop. Confirm message +
error roll-up adapt to selection size.
docs/web-ui.md updated to match.
1656b265ed