Based on #1425 


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---

> [!NOTE]
> Adds a floating scroll-to-bottom button and refines scroll/auto-scroll
behavior with layout tweaks to support an overlay.
> 
> - **Chat UI**:
> - **Scroll-to-bottom button**: Adds floating button in `ChatPanel`
(uses `Button` and `ArrowDown`) that appears when scrolled away and
scrolls smoothly to the latest message.
> - **Scroll logic**: Introduces `getDistanceFromBottom`,
`isNearBottom`, and a `scrollAwayThreshold`; auto-scroll now triggers
only when near the bottom; refactors `handleScroll` with `useCallback`
and longer idle timeout.
> - **Layout**: Wraps `MessagesList` in a `relative` container and
renders a centered absolute button overlay; adjusts `MessagesList` root
to `absolute inset-0` for proper overlay behavior.
> - **Misc**: Updates effect dependencies and console log message
related to streaming/scrolling.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
2e1b844830ae26cfc40840b9e8216fefad112a5e. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->
Co-authored-by: Md Rakibul Islam Rocky <mdrirocky08@outlook.com>