优化用户登录逻辑

src/main/java/com/onekeycall/videotablet/service/UserService.java

@@ -31,7 +31,7 @@ public class UserService implements UserDetailsService {
     }
 
     public User getUserByPhone(String phone) {
-        return userRepository.findUserByPhone(phone).orElseThrow(() -> new RuntimeException("User not found with phone: " + phone));
+        return userRepository.findUserByPhone(phone).orElse(null);
     }
 
     public User registerUser(String userId, String password) {