feat: 친구 라우터 작성 (#8)

routes/friend.js

+const express = require('express');
+const router = express.Router();
+const { isLoggedIn } = require('../middlewares/auth');
+const FriendController = require('../controllers/friendController');
+
+router.use(isLoggedIn);
+
+/**
+ * 친구 요청 보내기
+ * POST /api/friend/request
+ */
+router.post('/request', FriendController.sendRequest);
+
+/**
+ * 받은 친구 요청 목록 조회
+ * GET /api/friend/requests/received
+ */
+router.get('/requests/received', FriendController.getReceivedRequests);
+
+/**
+ * 보낸 친구 요청 목록 조회
+ * GET /api/friend/requests/sent
+ */
+router.get('/requests/sent', FriendController.getSentRequests);
+
+/**
+ * 친구 요청 수락
+ * POST /api/friend/request/:requestId/accept
+ */
+router.post('/request/:requestId/accept', FriendController.acceptRequest);
+
+/**
+ * 친구 요청 거절
+ * POST /api/friend/request/:requestId/reject
+ */
+router.post('/request/:requestId/reject', FriendController.rejectRequest);
+
+/**
+ * 친구 목록 조회
+ * GET /api/friend/all
+ */
+router.get('/all', FriendController.getFriendList);
+
+/**
+ * 친구 삭제
+ * DELETE /api/friend/:friendId
+ */
+router.delete('/:friendId', FriendController.deleteFriend);
+
+module.exports = router;
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