chore(ci): remove retired Codex review workflows

[Pigbibi]

Summary

• remove the manually disabled Codex PR Review and Codex Review Gate workflows
• remove their dedicated gate script, policy, test coverage, Ruff override, and stale architecture gate statement
• retain active CI (test) and the unrelated reusable drift/AIAuditBridge workflow

Validation

• actionlint
• python3 -m ruff check .
• PYTHONPATH=src python3 -m pytest -q tests/test_notification_redaction.py
• PYTHONPATH=src python3 -m pytest -q tests (952 passed, 1 skipped)
• python3 -m compileall -q src tests scripts
• python3 -m pip wheel --no-deps .
• diff, scope, and secret checks

Safety evidence

• Repository ruleset and branch protection require only the GitHub Actions test check.
• Both removed workflows were disabled_manually; no local or organization code-search caller remained.
• No deploy, runtime, strategy, risk, evidence, manifest, or pin files changed.