Make crew picker linear: first slot, then "add another"

The Add/Remove/Done action menu was clunky. Replace it with a linear flow: configure a first worker (agent + model), print it, then ask "Add another worker?" — repeating until Done. The crew is always non-empty (a first slot is mandatory), so no empty-state handling, and duplicates still work (add the same agent again).

Removes the action-menu plumbing (promptCrewAction, crewSummary, promptCrewRemove, and the crewAction* consts); adds promptAddAnotherSlot. Slot removal is dropped — re-run entire review --configure to rebuild.