Persist upstream Radar review artifacts

[yvette-carlisle]

Summary

• refreshed the deterministic openai/codex upstream review queue
• added source-backed bundles, upstream reviews, upstream impacts, and social candidates for PRs 27961, 27541, and 27830
• kept Publisher work at social_candidate/v1 only; no social_post/v1 or X publishing

Validation

• cargo run -p decodex --bin decodex -- radar validate
• cargo run -p decodex --bin decodex -- radar bundle validate artifacts/github/bundles/openai-codex-pr-27961.json
• cargo run -p decodex --bin decodex -- radar bundle validate artifacts/github/bundles/openai-codex-pr-27541.json
• cargo run -p decodex --bin decodex -- radar bundle validate artifacts/github/bundles/openai-codex-pr-27830.json
• cargo make fmt
• cargo make lint-fix
• cargo make test