feat: Newsletter system improvements and validation framework

- Fix: Marketing events now display in Staff notifications tab
- Reorganize: Move Coupons to Marketing/Coupons for better organization
- Add: Comprehensive email/phone validation with extensible filter hooks
  - Email validation with regex pattern (xxxx@xxxx.xx)
  - Phone validation with WhatsApp verification support
  - Filter hooks for external API integration (QuickEmailVerification, etc.)
- Fix: Newsletter template routes now use centralized notification email builder
- Add: Validation.php class for reusable validation logic
- Add: VALIDATION_HOOKS.md documentation with integration examples
- Add: NEWSLETTER_CAMPAIGN_PLAN.md architecture for future campaign system
- Fix: API delete method call in Newsletter.tsx (delete -> del)
- Remove: Duplicate EmailTemplates.tsx (using notification system instead)
- Update: Newsletter controller to use centralized Validation class

Breaking changes:
- Coupons routes moved from /routes/Coupons to /routes/Marketing/Coupons
- Legacy /coupons routes maintained for backward compatibility

includes/Api/StoreController.php

@@ -268,17 +268,14 @@ class StoreController extends WP_REST_Controller {
      * @return WP_REST_Response|WP_Error Response object or error
      */
     public function get_customer_settings(WP_REST_Request $request) {
-        error_log('WooNooW: get_customer_settings called');
         try {
             $settings = CustomerSettingsProvider::get_settings();
-            error_log('WooNooW: Customer settings retrieved: ' . print_r($settings, true));
             
             $response = rest_ensure_response($settings);
             $response->header('Cache-Control', 'max-age=60');
             
             return $response;
         } catch (\Exception $e) {
-            error_log('WooNooW: get_customer_settings exception: ' . $e->getMessage());
             return new WP_Error(
                 'get_customer_settings_failed',
                 $e->getMessage(),