Reduce gap of chat messages stack and shrink copy button size (#7)
### TL;DR
Tightened up the chat UI with minor spacing and sizing adjustments.
### What changed?
- Added `gap="xs"` to the chat messages container so messages have smaller spacing between them.
- Reduced the copy button size from `icon` to `icon-xs` for a more compact appearance.
### How to test?
1. Open a chat conversation and verify that messages are evenly spaced with a small gap between them.
2. Hover over a message and confirm the copy button appears smaller and still functions correctly when clicked.
### Why make this change?
The chat message list had too much spacing between messages, and the copy button was visually oversized relative to the surrounding UI elements. These tweaks improve the overall visual polish and consistency of the chat interface.
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