Memory: add redline CI gate

[HhhBZzz]

Summary

• add a dedicated MemoryEffectivenessRedlineGateTest for hard redline gating
• add scripts/check-memory-redline-gate.sh as the local gate command
• add a narrow GitHub Actions workflow that runs the gate on PRs to codex/bootstrap-github
• add a policy test so the gate test, script, and workflow remain discoverable and enabled

Verification

• mvn -q -Dtest=MemoryRedlineGatePolicyTest,MemoryEffectivenessRedlineGateTest test
• scripts/check-memory-redline-gate.sh
• mvn -q -Dtest=MemoryEffectivenessRedlineGateTest,MemoryRedlineGatePolicyTest,MemoryEffectivenessRedlineReportServiceTest,MemoryEffectivenessRedlineTest test
• git diff --cached --check