refactor(admin): Migrate AdminAjaxHandler to Clean Architecture

- Move AdminAjaxHandler to Admin/Shared/Infrastructure/Api/Wordpress/
- Create FieldMapperInterface for decentralized field mapping
- Create FieldMapperRegistry for module discovery
- Create FieldMapperProvider for auto-registration of 12 mappers
- Add FieldMappers for all components:
  - ContactFormFieldMapper (46 fields)
  - CtaBoxSidebarFieldMapper (32 fields)
  - CtaLetsTalkFieldMapper
  - CtaPostFieldMapper
  - FeaturedImageFieldMapper (15 fields)
  - FooterFieldMapper (31 fields)
  - HeroFieldMapper
  - NavbarFieldMapper
  - RelatedPostFieldMapper (34 fields)
  - SocialShareFieldMapper
  - TableOfContentsFieldMapper
  - TopNotificationBarFieldMapper (17 fields)
- Update functions.php bootstrap with FieldMapperProvider
- AdminAjaxHandler reduced from ~700 to 145 lines
- Follows SRP, OCP, DIP principles

BACKUP BEFORE: Removing CTA A/B Testing legacy system

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

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

Admin/CtaBoxSidebar/Infrastructure/FieldMapping/CtaBoxSidebarFieldMapper.php

@@ -0,0 +1,76 @@
+<?php
+declare(strict_types=1);
+
+namespace ROITheme\Admin\CtaBoxSidebar\Infrastructure\FieldMapping;
+
+use ROITheme\Admin\Shared\Domain\Contracts\FieldMapperInterface;
+
+/**
+ * Field Mapper para CTA Box Sidebar
+ *
+ * RESPONSABILIDAD:
+ * - Mapear field IDs del formulario a atributos de BD
+ * - Solo conoce sus propios campos (modularidad)
+ *
+ * UBICACION:
+ * - Dentro del modulo CtaBoxSidebar (autocontenido)
+ * - Eliminar modulo = eliminar mapper
+ */
+final class CtaBoxSidebarFieldMapper implements FieldMapperInterface
+{
+    public function getComponentName(): string
+    {
+        return 'cta-box-sidebar';
+    }
+
+    public function getFieldMapping(): array
+    {
+        return [
+            // Visibility
+            'ctaEnabled' => ['group' => 'visibility', 'attribute' => 'is_enabled'],
+            'ctaShowOnDesktop' => ['group' => 'visibility', 'attribute' => 'show_on_desktop'],
+            'ctaShowOnMobile' => ['group' => 'visibility', 'attribute' => 'show_on_mobile'],
+            'ctaShowOnPages' => ['group' => 'visibility', 'attribute' => 'show_on_pages'],
+
+            // Content
+            'ctaTitle' => ['group' => 'content', 'attribute' => 'title'],
+            'ctaDescription' => ['group' => 'content', 'attribute' => 'description'],
+            'ctaButtonText' => ['group' => 'content', 'attribute' => 'button_text'],
+            'ctaButtonIcon' => ['group' => 'content', 'attribute' => 'button_icon'],
+            'ctaButtonAction' => ['group' => 'content', 'attribute' => 'button_action'],
+            'ctaButtonLink' => ['group' => 'content', 'attribute' => 'button_link'],
+
+            // Behavior
+            'ctaTextAlign' => ['group' => 'behavior', 'attribute' => 'text_align'],
+
+            // Typography
+            'ctaTitleFontSize' => ['group' => 'typography', 'attribute' => 'title_font_size'],
+            'ctaTitleFontWeight' => ['group' => 'typography', 'attribute' => 'title_font_weight'],
+            'ctaDescFontSize' => ['group' => 'typography', 'attribute' => 'description_font_size'],
+            'ctaButtonFontSize' => ['group' => 'typography', 'attribute' => 'button_font_size'],
+            'ctaButtonFontWeight' => ['group' => 'typography', 'attribute' => 'button_font_weight'],
+
+            // Colors
+            'ctaBackgroundColor' => ['group' => 'colors', 'attribute' => 'background_color'],
+            'ctaTitleColor' => ['group' => 'colors', 'attribute' => 'title_color'],
+            'ctaDescriptionColor' => ['group' => 'colors', 'attribute' => 'description_color'],
+            'ctaButtonBgColor' => ['group' => 'colors', 'attribute' => 'button_background_color'],
+            'ctaButtonTextColor' => ['group' => 'colors', 'attribute' => 'button_text_color'],
+            'ctaButtonHoverBg' => ['group' => 'colors', 'attribute' => 'button_hover_background'],
+            'ctaButtonHoverText' => ['group' => 'colors', 'attribute' => 'button_hover_text_color'],
+
+            // Spacing
+            'ctaContainerPadding' => ['group' => 'spacing', 'attribute' => 'container_padding'],
+            'ctaTitleMarginBottom' => ['group' => 'spacing', 'attribute' => 'title_margin_bottom'],
+            'ctaDescMarginBottom' => ['group' => 'spacing', 'attribute' => 'description_margin_bottom'],
+            'ctaButtonPadding' => ['group' => 'spacing', 'attribute' => 'button_padding'],
+            'ctaIconMarginRight' => ['group' => 'spacing', 'attribute' => 'icon_margin_right'],
+
+            // Visual Effects
+            'ctaBorderRadius' => ['group' => 'visual_effects', 'attribute' => 'border_radius'],
+            'ctaButtonBorderRadius' => ['group' => 'visual_effects', 'attribute' => 'button_border_radius'],
+            'ctaBoxShadow' => ['group' => 'visual_effects', 'attribute' => 'box_shadow'],
+            'ctaTransitionDuration' => ['group' => 'visual_effects', 'attribute' => 'transition_duration'],
+        ];
+    }
+}