feat(theme): add [roi_post_grid] shortcode for static pages

- Create PostGridShortcodeRegistrar for WordPress shortcode registration
- Implement RenderPostGridUseCase following Clean Architecture
- Add PostGridQueryBuilder for custom WP_Query construction
- Add PostGridShortcodeRenderer for HTML/CSS generation
- Register shortcode in DIContainer with proper DI
- Add shortcode usage guide in post-grid admin panel
- Fix sidebar layout: add hide_for_logged_in check to wrapper visibility

Shortcode attributes: category, tag, author, posts_per_page, columns,
show_pagination, show_thumbnail, show_excerpt, show_meta, etc.

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

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

Shared/Infrastructure/Wordpress/PostGridShortcodeRegistrar.php

@@ -0,0 +1,95 @@
+<?php
+declare(strict_types=1);
+
+namespace ROITheme\Shared\Infrastructure\Wordpress;
+
+use ROITheme\Shared\Infrastructure\Di\DIContainer;
+use ROITheme\Shared\Application\UseCases\RenderPostGrid\RenderPostGridRequest;
+
+/**
+ * Registra el shortcode [roi_post_grid] en WordPress
+ *
+ * RESPONSABILIDAD:
+ * - Registrar shortcode via add_shortcode
+ * - Sanitizar atributos del shortcode
+ * - Delegar ejecucion a RenderPostGridUseCase
+ *
+ * NO RESPONSABLE DE:
+ * - Logica de negocio
+ * - Construccion de queries
+ * - Generacion de HTML/CSS
+ *
+ * @package ROITheme\Shared\Infrastructure\Wordpress
+ */
+final class PostGridShortcodeRegistrar
+{
+    private const SHORTCODE_TAG = 'roi_post_grid';
+
+    /**
+     * Registra el shortcode en WordPress
+     */
+    public static function register(): void
+    {
+        add_shortcode(self::SHORTCODE_TAG, [new self(), 'handleShortcode']);
+    }
+
+    /**
+     * Callback del shortcode
+     *
+     * @param array|string $atts Atributos del shortcode
+     * @return string HTML del grid
+     */
+    public function handleShortcode($atts): string
+    {
+        $atts = $this->sanitizeAttributes($atts);
+
+        // Obtener paged desde query var si existe
+        $id = $atts['id'] ?? '';
+        $queryVar = !empty($id) ? "paged_{$id}" : 'paged';
+        $atts['paged'] = max(1, (int) get_query_var($queryVar, 1));
+
+        // Crear request DTO
+        $request = RenderPostGridRequest::fromArray($atts);
+
+        // Obtener UseCase desde DIContainer
+        $container = DIContainer::getInstance();
+        $useCase = $container->getRenderPostGridUseCase();
+
+        return $useCase->execute($request);
+    }
+
+    /**
+     * Sanitiza atributos del shortcode
+     *
+     * @param array|string $atts
+     * @return array<string, mixed>
+     */
+    private function sanitizeAttributes($atts): array
+    {
+        $atts = shortcode_atts([
+            'category' => '',
+            'exclude_category' => '',
+            'tag' => '',
+            'author' => '',
+            'posts_per_page' => '9',
+            'columns' => '3',
+            'orderby' => 'date',
+            'order' => 'DESC',
+            'show_pagination' => 'false',
+            'offset' => '0',
+            'exclude_posts' => '',
+            'show_thumbnail' => 'true',
+            'show_excerpt' => 'true',
+            'show_meta' => 'true',
+            'show_categories' => 'true',
+            'excerpt_length' => '20',
+            'class' => '',
+            'id' => '',
+        ], $atts, self::SHORTCODE_TAG);
+
+        // Sanitizar cada valor
+        return array_map(function ($value) {
+            return is_string($value) ? sanitize_text_field($value) : $value;
+        }, $atts);
+    }
+}