Add Docker competitive parity gate

[yvette-carlisle]

Summary

• add a normative competitive parity gate spec for ELF adoption decisions
• add a Docker-only parity compose stack and runner that validates the agentmemory fixture adapter, service-backed consolidation/retrieval behavior, and admin viewer availability
• add Makefile entries and a runbook for running and cleaning the gate; update the README viewer comparison to match current main

What this proves

• The checked-in gate is a minimum executable floor, not proof that ELF is production-ready for personal use.
• Personal production adoption still requires the same Docker gate to pass on a private personal fixture pack and at least one live external baseline, starting with agentmemory.

Validation

• bash -n scripts/parity-docker-gate.sh scripts/consolidation-harness.sh
• docker compose -f docker-compose.parity.yml config
• git diff --check
• cargo make parity-docker
• jq -e ' .verdict == "pass" and .baselines.agentmemory_fixture.provenance_completeness == 1 and ([.dimensions | to_entries[] | select(.key != "cleanup" and .value.status != "pass")] | length == 0) ' tmp/parity/competitive-parity-report.json\n- cargo make parity-docker-clean\n- cargo make fmt-check