[RAPID-fix] REST API 메시지 전송 시 Socket.IO broadcast 추가

- socketManager.ts 모듈 생성 (io 전역 공유)
- sendMessage 컨트롤러에서 io.to(room).emit('new_message') broadcast
- 상대방 말풍선 너비 고정 수정 (items-start 추가)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend-node/src/app.ts

@@ -416,10 +416,12 @@ const server = app.listen(PORT, HOST, async () => {
   try {
     const { Server: SocketIOServer } = await import("socket.io");
     const { initMessengerSocket } = await import("./socket/messengerSocket");
+    const { setIo } = await import("./socket/socketManager");
     const io = new SocketIOServer(server, {
       cors: { origin: "*", methods: ["GET", "POST"] },
       path: "/socket.io",
     });
+    setIo(io);
     initMessengerSocket(io);
     logger.info("💬 Socket.IO messenger initialized");
   } catch (error) {

backend-node/src/controllers/messengerController.ts

@@ -1,6 +1,7 @@
 import { Request, Response } from 'express';
 import { messengerService } from '../services/messengerService';
 import { AuthenticatedRequest } from '../types/auth';
+import { getIo } from '../socket/socketManager';
 import path from 'path';
 
 class MessengerController {
@@ -69,6 +70,13 @@ class MessengerController {
       }
 
       const message = await messengerService.sendMessage(roomId, user.userId, user.companyCode!, content, messageType, parentId);
+
+      // Broadcast to all room participants via Socket.IO
+      const io = getIo();
+      if (io) {
+        io.to(`${user.companyCode}:${roomId}`).emit('new_message', message);
+      }
+
       res.json({ success: true, data: message });
     } catch (error) {
       const err = error as Error;

backend-node/src/socket/socketManager.ts

@@ -0,0 +1,11 @@
+import { Server } from 'socket.io';
+
+let _io: Server | null = null;
+
+export function setIo(io: Server) {
+  _io = io;
+}
+
+export function getIo(): Server | null {
+  return _io;
+}

frontend/components/messenger/MessageItem.tsx

@@ -53,7 +53,7 @@ export function MessageItem({ message, isOwn, showAvatar }: MessageItemProps) {
         <div className="w-7" />
       )}
 
-      <div className={cn("flex flex-col max-w-[70%]", isOwn && "items-end")}>
+      <div className={cn("flex flex-col max-w-[70%]", isOwn ? "items-end" : "items-start")}>
         {showAvatar && !isOwn && (
           <span className="text-xs font-medium text-muted-foreground mb-0.5">
             {message.senderName}