[RAPID] feat: 메신저 기능 구현 (Socket.IO 실시간 채팅)

- DB: messenger_rooms/participants/messages/reactions/files 테이블 생성
- Backend: REST API 9개 엔드포인트 + Socket.IO 실시간 핸들러
- Frontend: Gmail 스타일 FAB + 모달, 채팅방 목록, 채팅 패널
- 기능: DM/그룹/채널, 파일 첨부, 이모지 리액션, 멘션, 스레드
- 알림: 토스트 on/off 토글, FAB 읽지 않은 배지

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

[RAPID-fix] 메신저 API snake_case→camelCase 변환 및 Socket.IO URL 수정

- useRooms/useMessages/useCompanyUsers 훅에서 DB 응답 camelCase 변환
- Socket.IO 기본 연결 URL 3001 → 8080 수정
- runMigration.ts 마이그레이션 파일 경로 수정 (../../ → ../../../)

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

[RAPID-fix] 방 생성 API camelCase/snake_case 호환 처리

- createRoom 컨트롤러에서 participantIds/type/name (camelCase) fallback 추가

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

[RAPID-fix] 메시지 전송 API 추가 (sendMessage 라우트/컨트롤러 누락)

- POST /api/messenger/rooms/:roomId/messages 라우트 등록
- MessengerController.sendMessage 메서드 추가

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

backend-node/src/config/multerMessengerConfig.ts

@@ -0,0 +1,63 @@
+import multer from 'multer';
+import path from 'path';
+import fs from 'fs';
+
+// Upload directory
+const UPLOAD_DIR = process.env.NODE_ENV === 'production'
+  ? '/app/uploads/messenger-files'
+  : path.join(process.cwd(), 'uploads', 'messenger-files');
+
+// Create directory if not exists
+try {
+  if (!fs.existsSync(UPLOAD_DIR)) {
+    fs.mkdirSync(UPLOAD_DIR, { recursive: true });
+  }
+} catch (error) {
+  console.error('Messenger file upload directory creation failed:', error);
+}
+
+// File storage config
+const storage = multer.diskStorage({
+  destination: (req, file, cb) => {
+    cb(null, UPLOAD_DIR);
+  },
+  filename: (req, file, cb) => {
+    try {
+      file.originalname = file.originalname.normalize('NFC');
+      const uniqueId = Date.now() + '-' + Math.round(Math.random() * 1e9);
+      const ext = path.extname(file.originalname);
+      cb(null, `${uniqueId}${ext}`);
+    } catch (error) {
+      console.error('Filename processing error:', error);
+      cb(null, `${Date.now()}-${Math.round(Math.random() * 1e9)}_error.tmp`);
+    }
+  },
+});
+
+// File filter - block dangerous extensions
+const fileFilter = (req: any, file: Express.Multer.File, cb: multer.FileFilterCallback) => {
+  try {
+    file.originalname = file.originalname.normalize('NFC');
+  } catch (error) {
+    // ignore normalization failure
+  }
+
+  const dangerousExtensions = ['.exe', '.bat', '.cmd', '.sh', '.ps1', '.msi'];
+  const ext = path.extname(file.originalname).toLowerCase();
+
+  if (dangerousExtensions.includes(ext)) {
+    cb(new Error(`Security: ${ext} files are not allowed.`));
+    return;
+  }
+
+  cb(null, true);
+};
+
+export const uploadMessengerFile = multer({
+  storage,
+  fileFilter,
+  limits: {
+    fileSize: 20 * 1024 * 1024, // 20MB
+    files: 10,
+  },
+});