v1.2.0 — agent spawning

Agent spawning (hallpass.agents). The orchestrator can now create scoped agents, not just dispatch to existing ones. Team.spawn(AgentSpec) mints each agent a token carrying only its harness scopes and launches it through a pluggable Spawner (default SubprocessSpawner), passing name/token/task/channel by env; AgentContext.from_env() picks it up inside the process. Each spawned agent is a scoped identity, not a trusted one. Model-agnostic: the loop inside is yours. Demos in examples/spawn_agents.py.