Do not lock scroll position while text is streaming

[benjaminshafii]

Problem

While assistant text is streaming, the conversation view appears to stay pinned to the live output. That makes it hard to scroll up and read earlier content while a response is still coming in.

Expected behavior

• Users can freely scroll up while text is streaming without the view snapping back to the latest token.
• Auto-follow should only happen when the user is already at or near the bottom, or after an explicit jump back to the latest message.
• Streaming should not fight manual scroll position.

Why this matters

This makes long responses easier to review in real time and avoids a frustrating "scroll lock" feeling in the chat UI.

[AshhKetchup]

Hi! I've opened a pr that addresses this issue. Please take a look when you have a moment.
thanks!

[benjaminshafii]

Assigning @jcllobet to verify the current fix end-to-end, especially the work in PR #1096.