[BE][Feat] : #42 : 로그인 api 구현

- 로그인을 위한 패키지 (bcrypt, express-validator, jsonwebtoken) 설치
- 로그인을 위한 router, controller, service, repository, middleware 구현
- index.js router 호출 및 사용
- 로그인 api 구현 테스트

backend/src/routes/authRouter.js

@@ -0,0 +1,18 @@
+import express from 'express';
+import { body } from 'express-validator';
+import { login } from '../controllers/authController.js';
+import validationMiddleware from '../middleware/validationMiddleware.js';
+
+export const router = express.Router();
+
+router.post(
+  '/login',
+  [
+    body('id').notEmpty().withMessage('ID is required'),
+    body('password')
+      .isLength({ min: 6 })
+      .withMessage('Password must be at least 6 characters long'),
+  ],
+  validationMiddleware,
+  login,
+);