refactor: 로그아웃 postmapping 오타 수정

src/backend/auth-server/src/main/java/com/lalala/auth/controller/AuthController.java

@@ -32,7 +32,7 @@ public ResponseEntity<UserAndTokenResponse> singInUser(
         return authService.signIn(request);
     }
 
-    @PostMapping("signout")
+    @PostMapping("/signout")
     public ResponseEntity<Boolean> signOutUser(HttpServletRequest request) {
         return authService.signOut(request);
     }