Add cycle health summary command

[ozand]

Summary

• add read-only cycle health summary builder and CLI command
• include latest cycle/report/subagent telemetry, systemd bridge status, failed unit count, promotion readiness, and next recommended action
• document eeepc operator usage

Validation

• python -m py_compile nanobot/runtime/health.py eeebot/runtime/health.py nanobot/cli/commands.py tests/test_cycle_health_summary.py nanobot/runtime/state.py
• manual health summary unit probe with fake runtime state/systemd
• uv pytest attempted but blocked by PyPI hatchling TLS/connect timeout
• read-only SSH probe on eeepc: bridge last run 0/SUCCESS, failed units 0, telemetry landing in canonical state/subagents