feat: show loading message and scroll to buttom in chatroom

[howard9199]

This pull request includes several enhancements and bug fixes to the Chatroom.svelte component. The changes improve the user experience by adding new features and fixing existing issues.

Enhancements to Chatroom.svelte:

• Added a new isIndividual property to the Chatroom component to handle individual chat sessions.
• Introduced an animated dots feature to indicate ongoing processing or thinking, which updates every 500 milliseconds.
• Implemented a new UI element to display a loading message with animated dots when the last message in an individual conversation is from the user.

Bug fixes and minor improvements:

• Changed the scrollToBottom function to use requestAnimationFrame for smoother scrolling and added a delay using setTimeout to ensure it scrolls correctly.
• Adjusted the minimum height of the Textarea component to improve the layout.

Updates to ParticipantView.svelte:

• Passed the new isIndividual property to the Chatroom component when the session status is 'individual'.