Add Codex Radar publisher workflow

[yvette-carlisle]

Summary

• Add continuous Codex Radar workflow contracts, repo-local dev skills, upstream-impact and social draft schemas.
• Add local Radar SQLite ledger, 28-day raw artifact retention policy, and archive manifest/runbook surfaces.
• Curate the public site feed for community-ready signals and keep release-delta comparisons honest when the latest pair has no tracked signal evidence.

Validation

• cargo make decodex-checks
• python3 scripts/github/test_build_release_delta.py
• python3 scripts/github/test_backfill_release_range.py
• python3 scripts/github/test_radar_ledger.py
• python3 -m py_compile scripts/github/build_release_delta.py scripts/github/backfill_release_range.py scripts/github/radar_ledger.py scripts/github/sync_latest_signals.py scripts/github/test_build_release_delta.py scripts/github/test_backfill_release_range.py scripts/github/test_radar_ledger.py
• python3 scripts/github/sync_latest_signals.py --repo openai/codex --search-limit 1 --max-new-prs 0

Notes

• Manual-authority publisher infrastructure change.
• Follow-up sync/archive data update should happen after this lands.