fix(tui): preserve active session after provider logout

[sailist]

Related Issue

No linked GitHub issue; this fixes the tracked provider logout session regression.

Problem

Logging out of the provider used by the active TUI session cleared the selected model and closed the session. This discarded usable session state and prevented persisted model aliases from following the existing resume behavior.

What changed

• Keep the active TUI session open when a provider is removed or logged out.
• Refresh the provider and model catalogs without clearing session-owned runtime state.
• Continue clearing config-derived model state when no session exists, so new sessions still require an explicitly configured model.
• Cover active-session and session-less logout behavior with regression tests.

Checklist

• I have read the CONTRIBUTING document.
• I have linked a related issue (external PRs: the issue must have a maintainer's /approve).
• 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: 56446cb

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	Patch

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commit: 56446cb