Declare worker-health AIGuard evidence candidate

[hyeokjun32]

Summary

• add edgeenv_orchestrator_worker_health_trend to the EdgeEnv/AIGuard evidence candidate list emitted by Orchestrator sustained feeds
• keep downstream guard alignment and mapping hints consistent with the existing worker_health_trend summary block
• update README wording and contract-checker tests for the expanded candidate list

Tests

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