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>

functions.php

@@ -126,8 +126,16 @@ try {
     // Obtener Use Case para guardar configuraciones
     $saveComponentSettingsUseCase = $container?->getSaveComponentSettingsUseCase();
 
-    // Crear y registrar el handler AJAX con inyección del Use Case
-    $adminAjaxHandler = new \ROITheme\Admin\Infrastructure\Api\Wordpress\AdminAjaxHandler($saveComponentSettingsUseCase);
+    // === FIELD MAPPER REGISTRY (Auto-registro escalable) ===
+    $fieldMapperRegistry = new \ROITheme\Admin\Shared\Infrastructure\FieldMapping\FieldMapperRegistry();
+    $fieldMapperProvider = new \ROITheme\Admin\Shared\Infrastructure\FieldMapping\FieldMapperProvider($fieldMapperRegistry);
+    $fieldMapperProvider->registerAll();
+
+    // === ADMIN AJAX HANDLER ===
+    $adminAjaxHandler = new \ROITheme\Admin\Shared\Infrastructure\Api\Wordpress\AdminAjaxHandler(
+        $saveComponentSettingsUseCase,
+        $fieldMapperRegistry
+    );
     $adminAjaxHandler->register();
 
     // Crear y registrar el handler AJAX para el Contact Form (público)