fix(tui): preserve native scrollback on terminal resize

[joinmouse]

Related Issue

Related Issue

Fixes #3116

#3116

Problem

Resizing the terminal window could clear the native scrollback buffer and change the user's current scroll position.

This was especially noticeable when the user had scrolled away from the input area: resizing either the terminal width or height could unexpectedly move the
viewport to the top of the conversation.

What changed

• Preserve native terminal scrollback during terminal resize.
• Keep height changes on the differential rendering path instead of performing a full redraw.
• On width changes, clear and redraw only the active viewport rather than clearing scrollback or replaying the entire transcript.
• Preserve the existing full-redraw behavior for explicit render resets and Kitty image handling.
• Add regression tests covering:
  • Height changes without clearing scrollback.
  • Width changes without duplicating transcript history.
  • Width changes while the user is manually scrolled away from the prompt.

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: dc82089

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/pi-tui	Patch
@moonshot-ai/kimi-code	Patch

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[chatgpt-codex-connector]

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[HelloWorldU]

We should not change current behaviors as it may lead to regression