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/Application/UseCases/RenderPostGrid/RenderPostGridUseCase.php

@@ -0,0 +1,71 @@
+<?php
+declare(strict_types=1);
+
+namespace ROITheme\Shared\Application\UseCases\RenderPostGrid;
+
+use ROITheme\Shared\Domain\Contracts\PostGridQueryBuilderInterface;
+use ROITheme\Shared\Domain\Contracts\PostGridShortcodeRendererInterface;
+use ROITheme\Shared\Domain\Contracts\ComponentSettingsRepositoryInterface;
+use ROITheme\Shared\Domain\Constants\VisibilityDefaults;
+
+/**
+ * Caso de uso: Renderizar grid de posts para shortcode
+ *
+ * RESPONSABILIDAD: Orquestar la obtencion de settings, construccion de query
+ * y renderizado del grid. No contiene logica de negocio, solo coordinacion.
+ *
+ * @package ROITheme\Shared\Application\UseCases\RenderPostGrid
+ */
+final class RenderPostGridUseCase
+{
+    private const COMPONENT_NAME = 'post-grid';
+
+    public function __construct(
+        private readonly PostGridQueryBuilderInterface $queryBuilder,
+        private readonly PostGridShortcodeRendererInterface $renderer,
+        private readonly ComponentSettingsRepositoryInterface $settingsRepository
+    ) {}
+
+    /**
+     * Ejecuta el caso de uso: obtiene settings, construye query y renderiza
+     *
+     * @param RenderPostGridRequest $request DTO con atributos del shortcode
+     * @return string HTML del grid renderizado
+     */
+    public function execute(RenderPostGridRequest $request): string
+    {
+        // 1. Obtener settings del componente post-grid desde BD
+        $settings = $this->getSettings();
+
+        // 2. Construir query con los parametros del shortcode
+        $query = $this->queryBuilder->build($request->toQueryParams());
+
+        // 3. Renderizar grid con query, settings y opciones
+        $html = $this->renderer->render(
+            $query,
+            $settings,
+            $request->toRenderOptions()
+        );
+
+        // 4. Limpiar query (importante para evitar conflictos)
+        wp_reset_postdata();
+
+        return $html;
+    }
+
+    /**
+     * Obtiene settings del componente post-grid
+     *
+     * @return array<string, mixed>
+     */
+    private function getSettings(): array
+    {
+        $settings = $this->settingsRepository->getComponentSettings(self::COMPONENT_NAME);
+
+        if (empty($settings)) {
+            return VisibilityDefaults::getForComponent(self::COMPONENT_NAME);
+        }
+
+        return $settings;
+    }
+}