Add worker health trend summary

[hyeokjun32]

Summary:

• add a supplemental worker_health_trend block to the sustained operation timeline summary
• mirror the trend through the EdgeEnv telemetry feed via operation_timeline_summary
• validate scheduler/lab ownership markers so the block remains operation evidence, not a deployment decision
• document the additive field in English/Korean orchestration-summary contract docs

Tests:

• python -m pytest tests/test_multi_workload_sustained.py -q
• python -m pytest -q
• git diff --check