style(chat): adjust spacing and margins in chat components

- Reduce gap between elements in BaseChat component from `gap-4` to `gap-2`
- Remove bottom margin from AssistantMessage component for cleaner layout
- Add expo.svg icon to the icons directory for future use

app/components/chat/BaseChat.tsx

@@ -375,7 +375,7 @@ export const BaseChat = React.forwardRef<HTMLDivElement, BaseChatProps>(
                 />
               )}
               <div
-                className={classNames('flex flex-col gap-4 w-full max-w-chat mx-auto z-prompt mb-6', {
+                className={classNames('flex flex-col gap-2 w-full max-w-chat mx-auto z-prompt mb-6', {
                   'sticky bottom-2': chatStarted,
                 })}
               >