Fix: Rename class files and apply coding standard fixes

admin/lib/admin.php

@@ -1 +1,7 @@
 <?php
+/**
+ * Admin area specific functions.
+ *
+ * @package WPALLSTARS\PluginStarterTemplate\Admin\Lib
+ * @file
+ */

admin/lib/modal.php

@@ -1 +1,14 @@
 <?php
+/**
+ * Modal related functions for the admin area.
+ *
+ * @package WPALLSTARS\PluginStarterTemplate\Admin\Lib
+ */
+
+/**
+ * File: modal.php
+ * Description: Modal related functions for the admin area.
+ * Version: 1.0
+ * Author: Your Name
+ * Author URI: https://yourwebsite.com
+ */