Record decision trace eval ownership boundary

[YSCJRH]

Summary

• add a post-Phase-67 decision-trace eval-ownership boundary note
• record that eval-owned decision-trace replay metrics remain unclaimed and are not a current Phase 68 blocker
• sync current-state docs and tests so this follow-up stays a paused stop-state, not an implementation queue

Validation

• python -m pytest backend/tests/test_post_phase67_decision_trace_eval_ownership_boundary.py -q
• python -m pytest backend/tests/test_post_phase67_decision_trace_replay_audit.py backend/tests/test_post_phase67_decision_trace_eval_ownership_boundary.py -q
• python -m pytest backend/tests/test_post_phase67_successor_intake_audit.py backend/tests/test_post_phase67_outcome_eval_audit.py backend/tests/test_post_phase67_runtime_created_world_eval_proof.py backend/tests/test_post_phase67_decision_trace_replay_audit.py backend/tests/test_post_phase67_decision_trace_eval_ownership_boundary.py -q
• python scripts/check_no_secrets.py
• python -m backend.app.cli audit-github-queue --repo YSCJRH/mirror-sim
• git diff --check

Review

• Read-only subagent final review found no blockers and recommended safe to commit, PR, and auto-merge once CI is green.