♻️ refactor: 리다이렉트 문자열 변수로 분리

Author: jiwon1217

backend/src/main/java/io/f1/backend/domain/user/app/handler/OAuthSuccessHandler.java

@@ -25,9 +25,11 @@ public void onAuthenticationSuccess(
         response.setContentType("application/json;charset=UTF-8");
 
         if (principal.getUserNickname() == null) {
-            getRedirectStrategy().sendRedirect(request, response, "http://localhost:3000/signup");
+            String SIGNUP_REDIRECT_URL = "http://localhost:3000/signup";
+            getRedirectStrategy().sendRedirect(request, response, SIGNUP_REDIRECT_URL);
         } else {
-            getRedirectStrategy().sendRedirect(request, response, "http://localhost:3000/room");
+            String MAIN_REDIRECT_URL = "http://localhost:3000/room";
+            getRedirectStrategy().sendRedirect(request, response, MAIN_REDIRECT_URL);
         }
     }
 }