Refactor database seeder to use config for admin credentials and add admin configuration file

config/admin.php

@@ -0,0 +1,7 @@
+<?php
+
+return [
+    'name' => env('ADMIN_NAME', 'Admin'),
+    'email' => env('ADMIN_EMAIL', 'admin@example.com'),
+    'password' => env('ADMIN_PASSWORD', 'changeme123'),
+];