refactor: share workflow addressed sends

[shuxueshuxue]

Summary

• route group workflow notifications through the shared addressed message sender
• remove warning-only swallowed send failures from workflow notify loops
• add boundary tests that prevent direct workflow chat sends and swallowed send errors

Verification

• uv run pytest tests/test_boundary.py::test_group_workflow_notify_does_not_send_chat_directly tests/test_boundary.py::test_group_workflow_notify_does_not_swallow_send_errors tests/test_group_chat_transport.py tests/test_daemon_subscriber.py tests/test_daemon_ipc.py -q
• uv run pytest -q
• uv run ruff check packages/mycel-cli/src tests/test_boundary.py
• uv run ruff format --check packages/mycel-cli/src tests/test_boundary.py