Refactor plugin structure and remove legacy admin code

Removed old admin controllers, interfaces, AJAX handlers, and partials. Introduced new classes in the includes directory for admin, config, frontend, loader, output manager, and validator. Updated asset files and main plugin entry point to use the new structure. Cleaned up obsolete files and improved overall maintainability.

includes/class-frontend.php

@@ -0,0 +1,69 @@
+<?php
+
+namespace WPTag;
+
+if (!defined('ABSPATH')) {
+    exit;
+}
+
+class Frontend {
+    private $config;
+    private $output_manager;
+
+    public function __construct($config) {
+        $this->config = $config;
+        $this->output_manager = new Output_Manager($config);
+        
+        $this->init_hooks();
+    }
+
+    private function init_hooks() {
+        add_action('wp_head', array($this, 'output_head_codes'), 1);
+        add_action('wp_body_open', array($this, 'output_body_codes'), 1);
+        add_action('wp_footer', array($this, 'output_footer_codes'), 1);
+        add_action('wp_enqueue_scripts', array($this, 'enqueue_frontend_assets'));
+    }
+
+    public function output_head_codes() {
+        if (!$this->should_output_codes()) {
+            return;
+        }
+        
+        $this->output_manager->output_codes('head');
+    }
+
+    public function output_body_codes() {
+        if (!$this->should_output_codes()) {
+            return;
+        }
+        
+        $this->output_manager->output_codes('body');
+    }
+
+    public function output_footer_codes() {
+        if (!$this->should_output_codes()) {
+            return;
+        }
+        
+        $this->output_manager->output_codes('footer');
+    }
+
+    private function should_output_codes() {
+        if (is_admin()) {
+            return false;
+        }
+        
+        if (is_user_logged_in() && current_user_can('manage_options')) {
+            $show_for_admin = apply_filters('wptag_show_for_admin', false);
+            if (!$show_for_admin) {
+                return false;
+            }
+        }
+        
+        return apply_filters('wptag_should_output_codes', true);
+    }
+
+    public function enqueue_frontend_assets() {
+        do_action('wptag_enqueue_frontend_assets');
+    }
+}