Fix: Rename class files and apply coding standard fixes

includes/class-core.php

@@ -0,0 +1,31 @@
+<?php
+/**
+ * Core functionality for the plugin
+ *
+ * @package WPALLSTARS\PluginStarterTemplate
+ */
+
+namespace WPALLSTARS\PluginStarterTemplate;
+
+/**
+ * Core class
+ */
+class Core {
+
+	/**
+	 * Constructor
+	 */
+	public function __construct() {
+		// Initialize hooks.
+	}
+
+	/**
+	 * Example method to filter content
+	 *
+	 * @param string $content The content to filter.
+	 * @return string The filtered content.
+	 */
+	public function filter_content( $content ) {
+		return $content;
+	}
+}