fix(analytics): Corregir URLs en analytics usando post_name desde BD

Problema:
- URLs en analytics mostraban dominio incorrecto (HTTP_HOST)
- URLs usaban formato /?p=ID en lugar de permalinks

Solución:
- class-search-engine.php: Agregar propiedad $prefix, incluir p.post_name
  en 5 queries fetch, agregar helpers getSiteUrlFromDb(),
  getPermalinkStructure() y buildPermalink()
- search-endpoint.php: Obtener site_url y permalink_structure desde
  wp_options, construir URLs con post_name
- click-endpoint.php: Fallback de dest usando post_name desde BD

Archivos modificados:
- includes/class-search-engine.php
- api/search-endpoint.php
- api/click-endpoint.php

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

includes/class-db-connection.php

@@ -0,0 +1,120 @@
+<?php
+/**
+ * Database Connection with PDO Persistent
+ *
+ * @package ROI_APU_Search
+ */
+
+declare(strict_types=1);
+
+// Prevent direct access
+if (!defined('ABSPATH')) {
+    exit;
+}
+
+/**
+ * Singleton class for PDO database connection with persistent connections
+ */
+final class ROI_APU_Search_DB
+{
+    private static ?self $instance = null;
+    private ?PDO $pdo = null;
+
+    /**
+     * Get singleton instance
+     */
+    public static function get_instance(): self
+    {
+        if (self::$instance === null) {
+            self::$instance = new self();
+        }
+        return self::$instance;
+    }
+
+    /**
+     * Private constructor
+     */
+    private function __construct()
+    {
+        $this->connect();
+    }
+
+    /**
+     * Establish PDO connection with persistent connection enabled
+     */
+    private function connect(): void
+    {
+        if ($this->pdo !== null) {
+            return;
+        }
+
+        // Get WordPress database credentials
+        $host = DB_HOST;
+        $name = DB_NAME;
+        $user = DB_USER;
+        $pass = DB_PASSWORD;
+        $charset = defined('DB_CHARSET') ? DB_CHARSET : 'utf8mb4';
+
+        // Handle port in host
+        $port = 3306;
+        if (strpos($host, ':') !== false) {
+            [$host, $port] = explode(':', $host);
+            $port = (int) $port;
+        }
+
+        $dsn = "mysql:host={$host};port={$port};dbname={$name};charset={$charset}";
+
+        $options = [
+            PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
+            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
+            PDO::ATTR_EMULATE_PREPARES   => true, // Same as original buscar-apus (enables reusing :q placeholder)
+            PDO::ATTR_PERSISTENT         => true, // Enable persistent connections
+        ];
+
+        try {
+            $this->pdo = new PDO($dsn, $user, $pass, $options);
+
+            // Set MySQL specific options (same as original buscar-apus)
+            $this->pdo->exec("SET NAMES {$charset} COLLATE {$charset}_unicode_ci");
+        } catch (PDOException $e) {
+            // Log error but don't expose details
+            error_log('ROI APU Search DB Error: ' . $e->getMessage());
+            throw new RuntimeException('Database connection failed');
+        }
+    }
+
+    /**
+     * Get the PDO instance
+     */
+    public function get_pdo(): PDO
+    {
+        if ($this->pdo === null) {
+            $this->connect();
+        }
+        return $this->pdo;
+    }
+
+    /**
+     * Get WordPress table prefix
+     */
+    public function get_prefix(): string
+    {
+        global $table_prefix;
+        return $table_prefix ?? 'wp_';
+    }
+
+    /**
+     * Prevent cloning
+     */
+    private function __clone()
+    {
+    }
+
+    /**
+     * Prevent unserialization
+     */
+    public function __wakeup()
+    {
+        throw new RuntimeException('Cannot unserialize singleton');
+    }
+}