feat: complete Newsletter Campaigns Phase 1

- Add default campaign email template to DefaultTemplates.php
- Add toggle settings (campaign_scheduling, subscriber_limit_enabled)
- Add public unsubscribe endpoint with secure token verification
- Update CampaignManager to use NewsletterController unsubscribe URLs
- Add generate_unsubscribe_url() helper for email templates

includes/Core/Campaigns/CampaignManager.php

@@ -428,12 +428,8 @@ class CampaignManager {
      * @return string
      */
     private static function get_unsubscribe_url($email) {
-        $token = wp_hash($email . 'woonoow_unsubscribe');
-        return add_query_arg([
-            'woonoow_unsubscribe' => 1,
-            'email' => urlencode($email),
-            'token' => $token,
-        ], home_url());
+        // Use NewsletterController's secure token-based URL
+        return \WooNooW\API\NewsletterController::generate_unsubscribe_url($email);
     }
     
     /**