fix(oauth): switch default model on explicit login

[simonhx6]

Related Issue

Resolves #2151

Problem

After switching from Kimi Code OAuth to an API key, selecting Kimi Code OAuth from /login in a new session can leave the API key model as the default. The login appears successful, but requests continue to use the API key until the user logs out first.

What changed

• Preserve the current default during an explicit OAuth login only when it is still a valid managed Kimi Code model.
• Replace a non-managed API default when the user explicitly selects Kimi Code OAuth.
• Keep background model refresh behavior unchanged so it does not replace defaults from other providers.
• Add OAuth toolkit and SDK regression coverage for the persisted-token scenario while verifying that the existing API provider configuration is retained.
• Add patch changesets for the CLI and SDK. No public API signatures were changed.

Verification

• vitest run packages/oauth/test/toolkit.test.ts packages/oauth/test/managed-kimi-code.test.ts packages/node-sdk/test/auth-facade.test.ts — 84 tests passed.
• pnpm run build
• pnpm run lint
• pnpm run sherif
• CI-equivalent tsgo checks for the OAuth and SDK packages.

No documentation update is needed because this fix restores the existing provider-selection behavior and introduces no new command, option, or configuration.

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.

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[changeset-bot]

🦋 Changeset detected

Latest commit: 059cbe2

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

This PR includes changesets to release 2 packages

Name	Type
@moonshot-ai/kimi-code	Patch
@moonshot-ai/kimi-code-sdk	Patch

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