Add GPT-5.4 and GPT-5.3 Codex options

[franciskim]

Summary

• add codex-gpt-5.4 and codex-gpt-5.3-codex to the frontend model selector
• allow both model keys in the backend allowlist
• map the new UI keys to raw Codex model IDs in the worker model map

Verification

• bun run build
• started the backend stack locally with Docker and confirmed http://127.0.0.1:1337/v1/integration/frontend responds
• submitted dummy /v1/jobs/start requests with both new model keys and confirmed they pass model validation and reach the expected 412 openai_key is required path

Notes

• bun run lint still reports a pre-existing import-order issue in frontend/src/components/results/results-header.tsx unrelated to this change