[codex] Use model-advertised reasoning effort order

[aibrahim-oai]

Summary

• preserve the model catalog order for app-server supportedReasoningEfforts and document that client contract
• render TUI reasoning choices in the advertised order
• step reasoning shortcuts by adjacent list position instead of deriving order from known effort names
• anchor unsupported configured values to the advertised default, or the first option when needed
• remove canonical effort ordering helpers and the unused upgrade effort mapping

Validation

• just fmt
• Local tests and compilation were not run per request; relying on CI.

Stacked on #26444.

[aibrahim-oai]

This change is part of the following stack:

• [codex] Support model-defined reasoning efforts #26444
  • [codex] Use model-advertised reasoning effort order #26446 ◀

_{Change managed by git-spice.}

[aibrahim-oai]

@codex review this

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Keep them coming!

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[fcoury-oai]

Smoke tested that reasoning effort options preserve the model-advertised order and exact string values across app-server and TUI selection and shortcuts.

Code looks good as well, approved. 👍