fix: permit /error endpoint to show proper error messages

backend/src/main/java/com/rayhan/erp/config/WebSecurityConfig.java

@@ -60,6 +60,7 @@ public class WebSecurityConfig {
             .authorizeHttpRequests(auth -> auth
                 .requestMatchers("/api/auth/**").permitAll()
                 .requestMatchers("/api/test/**").permitAll()
+                .requestMatchers("/error").permitAll()
                 .anyRequest().authenticated()
             );