Implement auto-scroll to top of message for new chat messages

[brylie]

Related to #22

Implement auto-scroll to top of message for new chat messages.

• HTML Template Changes: Add hx-on attributes to the form element to trigger scroll behavior and add a JavaScript function scrollToMessage to handle scrolling in app/templates/chat.html.
• FastAPI Endpoint Update: Update the /chat endpoint in app/main.py to generate and return message IDs and modify the response HTML to include the message IDs.
• JavaScript Changes: Add a scrollToBottom function to handle auto-scrolling and call scrollToBottom after appending user messages and bot responses in app/static/script.js.
• CSS Changes: Ensure the chat container has proper scrolling behavior and add styles for smooth scrolling in app/static/styles.css.

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