Fix: some method changes

backend/src/article/article.js

backend/src/article/articleController.js

backend/src/article/articleService.js

backend/src/auth/authController.js

backend/src/db.js

backend/src/index.js

backend/src/user/user.js

backend/src/user/userService.js

frontend/src/App.js

frontend/src/pages/Main.js

frontend/src/pages/PostRead.js

frontend/src/pages/PostWrite.js