feat: add Runtime operation evidence blocks

[hyeokjun32]

Summary

• Added additive runtime_health_snapshot, runtime_error_classification, and runtime_events blocks to Runtime result JSON.
• Documented the operation evidence contract while keeping Runtime out of scheduling/deployment decision ownership.
• Added schema and agent-result tests for the new operation evidence blocks.

Validation

• bash scripts/smoke_default.sh
• python3 tests/test_manifest_compare_identity.py
• python3 tests/test_lab_result_schema.py
• python3 tests/test_agent_runtime_result_contract.py
• python3 -m unittest discover -s tests -p 'test_*.py'

Notes

• Existing Lab-compatible Runtime result fields remain unchanged.
• Timeout detection is not claimed; results explicitly record timeout_policy as not_configured and timeout_observed as false.