Run workflows and handoffs

Outcome: keep workflows deterministic and make agent transfer an explicit new run.

Handoff module: examples.handoff_agent

python examples/handoff_agent.py

Expected: researcher and writer runs both complete with one agent.handoff event carrying the reason and target run ID. Muru Workspace shows each run and the ordered transfer.

Workflow module: examples.workflow_agent

python examples/workflow_agent.py

Expected: research and summarize checkpoints and the summary “AgentMuru verified 2 facts.” Unknown target agents fail before a target run; workflow handler failures return a stable failure code after configured retries.

Qualified by tests/qualification/test_scenarios.py::test_handoff_scenario_runs_both_agents, test_workflow_scenario_returns_checkpoint_evidence, and focused handoff/workflow tests.