Scroll position jumps to top on new message arrival

### What happened?

When a new message is received from the
Gemini agent, the chat window
automatically scrolls to the very top,
losing the current scroll position. This
requires manually scrolling back down to
see the latest message.

**Steps to Reproduce:**
1. Start a conversation with the Gemini
agent.
2. Send enough messages so that the
conversation history creates a scrollbar
in the window.
3. Scroll down to view an earlier part of
the conversation.
4. Wait for the agent to send a new
message.

### What did you expect to happen?

The scroll position should remain where
it is, or ideally, gently scroll to the
new message at the bottom if the user was
already at the bottom. It should not jump
to the top of the conversation history.

**Actual Behavior:**
The scroll position immediately jumps to
the top of the chat history, forcing the
user to scroll down manually to read the
new message.

### Client information

* **CLI Version:** 0.1.14
* **Git Commit:** de968877 (local modifications)
* **Operating System:** linux v22.17.1
* **Sandbox Environment:** no sandbox
* **Model Version:** gemini-2.5-pro
* **Memory Usage:** 173.7 MB

### Login information

Google Account

### Anything else we need to know?

_No response_