feat(auth): add ChatGPT Plus/Pro OAuth provider

[qipenglin]

Related Issue

Resolves #1523

Problem

See linked issue.

What changed

• Add OpenAI device-code OAuth login for ChatGPT Plus/Pro subscriptions, including credential storage and token refresh.
• Fetch the account's available Codex model catalog after login, with a conservative built-in fallback when catalog discovery is unavailable.
• Configure the ChatGPT Codex request path with the required account headers and omit unsupported completion-budget parameters.
• Add focused OAuth and runtime-provider coverage, bilingual provider documentation, and a CLI changeset.

This integration uses the ChatGPT Codex backend rather than OpenAI API-key billing. Model visibility and metadata come from the authenticated account when available.

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue, or explained the problem above.
• I have added tests that prove my feature works.
• Ran gen-changesets skill, or this PR needs no changeset.
• Ran gen-docs skill, or this PR needs no doc update.

[changeset-bot]

🦋 Changeset detected

Latest commit: 4d824e7

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@moonshot-ai/kimi-code	Minor

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