채팅 오토스크롤링 추가

-import React, { useCallback, useContext, useEffect, useState } from 'react';
+import React, { useCallback, useContext, useEffect, useRef, useState } from 'react';
 import SocketContext from '../../contexts/SocketContext';
 import { MessageType, RawMessage } from '../common/types';
 import { ChatLine } from './ChatLine';
@@ -8,6 +8,7 @@ export const Chat: React.FC = () => {
   const socket = useContext(SocketContext);
   const [ input, setInput ] = useState('');
   const [ chatLines, setChatLines ] = useState<ChatData[]>([]);
+  const messageEndRef = useRef<HTMLDivElement | null>(null);
 
   useEffect(() => {
     socket.on(MessageType.ROOM_CHAT, (data: ChatData) => {
@@ -19,6 +20,12 @@ export const Chat: React.FC = () => {
     }
   }, []);
 
+  const handleAutoScroll = useCallback(() => {
+    messageEndRef.current?.scrollIntoView({ behavior: 'smooth' });
+  }, []);
+  
+  useEffect(handleAutoScroll, [chatLines])
+
   const handleEnter = useCallback((e: React.KeyboardEvent) => {
     if (e.key === 'Enter') {
       setChatLines([...chatLines, { sender: 'me', message: input }]);
@@ -37,6 +44,7 @@ export const Chat: React.FC = () => {
     <div className='w-5/12'>
       <div className='w-full h-80 rounded shadow flex flex-col items-center end'>
         {chatLines.map((line, i) => (<ChatLine key={16383+i} chatData={line}/>))}
+        <div ref={messageEndRef} />
       </div>
       <input className='w-full px-3 py-2 bg-white
                       placeholder-gray-400 text-gray-700 text-sm