[codex] fix(stage-gate): pin conductor log target

[scarmani]

Summary

• add a canonical Stage-Gate Conductor log resolver that pins duplicate log streams to [automation] Stage-Gate Conductor Log #8671
• document the prompt contract so conductor automation comments on the resolved issue and fails closed instead of creating another duplicate
• update stale [automation] Stage-Gate Conductor Log #7162 references and add focused regression coverage

Root cause

The conductor log target was selected by search/heuristics, so multiple open issues with the exact [automation] Stage-Gate Conductor Log title could split future comments or trigger a new issue when lookup degraded.

Validation

• ARAGORA_USE_SECRETS_MANAGER=0 pytest tests/ops/test_stage_gate_conductor_log.py
• ARAGORA_USE_SECRETS_MANAGER=0 pytest tests/test_prompt_path_guidance_docs.py
• bash scripts/automation_pr_preflight.sh origin/main HEAD
• live resolver check: [8671, 8402, 7162, 6763, 6432, 6216, 6096] -> 8671

Closes #8711