Gate ChatGPT user ID metrics to app surfaces

[ningyi-oai]

Summary

• add a ChatGPT user ID accessor in auth and thread it into OTLP metrics metadata
• gate user ID emission behind an app-only opt-in env and a narrow originator allowlist so standalone OSS CLI stays unchanged
• emit both enduser.id and user_id metric tags and add a focused metrics test

Tests

• cargo fmt --manifest-path codex-rs/Cargo.toml --all
• cargo test --manifest-path codex-rs/Cargo.toml -p codex-otel manager_attaches_chatgpt_user_id_tags_when_present (blocked in this fresh clone by git dependency fetch/setup)
• cargo test --manifest-path codex-rs/Cargo.toml -p codex-core app_originator_allowlist_for_chatgpt_user_id_metrics_is_narrow (blocked in this fresh clone by git dependency fetch/setup)

Notes

• Paired with openai/openai#726938 for the app-side opt-in env plumbing.

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