[FEATURE]: show optional estimated Codex token costs #35133

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Describe the enhancement you want to request

Codex/ChatGPT subscription auth currently reports marginal usage cost as $0.00, which matches the user's direct billing but makes it hard to compare usage against API-equivalent token costs.

Please add an opt-in setting that keeps $0.00 as the default for subscription auth, while allowing users to show estimated API-equivalent costs for Codex models when they explicitly enable it.