feat: Complete backend wiring for notification system

✅ Global System Toggle:
- Added GET/POST /notifications/system-mode endpoints
- Switch between WooNooW and WooCommerce notification systems
- Stored in: woonoow_notification_system_mode
- EmailManager::is_enabled() checks system mode
- NotificationManager checks mode before sending

✅ Template System Wired:
- Templates saved via API are used when sending
- EmailRenderer fetches templates from TemplateProvider
- Variables replaced automatically
- Markdown parsed (cards, buttons, images)
- Email customization applied (colors, logo, branding)

✅ Channel Toggle Wired:
- Frontend toggles saved to database
- NotificationManager::is_channel_enabled() checks before sending
- Email: woonoow_email_notifications_enabled
- Push: woonoow_push_notifications_enabled

✅ Event Toggle Wired:
- Per-event channel settings saved
- NotificationManager::is_event_channel_enabled() checks before sending
- Stored in: woonoow_notification_settings

✅ Email Sending Flow:
Event → EmailManager → Check System Mode → Check Channel Toggle
→ Check Event Toggle → EmailRenderer → Get Template → Replace Variables
→ Parse Markdown → Apply Branding → wp_mail() → Sent

✅ All Settings Applied:
- Template modifications saved and used
- Channel toggles respected
- Event toggles respected
- Global system mode respected
- Email customization applied
- Push settings applied

📋 Modified Files:
- NotificationsController.php: Added system-mode endpoints
- NotificationManager.php: Added system mode check, wired EmailRenderer
- EmailManager.php: Added is_enabled() check for system mode

🎯 Result: Complete end-to-end notification system fully functional

includes/Core/Notifications/EmailManager.php

@@ -66,20 +66,26 @@ class EmailManager {
 		add_action('woocommerce_product_set_stock', [$this, 'check_stock_levels'], 10, 1);
 	}
 	
+	/**
+	 * Check if WooNooW notification system is enabled
+	 * 
+	 * @return bool
+	 */
+	public static function is_enabled() {
+		// Check global notification system mode
+		$system_mode = get_option('woonoow_notification_system_mode', 'woonoow');
+		return $system_mode === 'woonoow';
+	}
+	
 	/**
 	 * Disable WooCommerce default emails
 	 * 
 	 * @param WC_Emails $email_class
 	 */
 	public function disable_wc_emails($email_class) {
-		// Get WooNooW notification settings
-		$settings = get_option('woonoow_notification_settings', []);
-		
-		// Check if custom emails are enabled (default: yes)
-		$use_custom_emails = $settings['use_custom_emails'] ?? true;
-		
-		if (!$use_custom_emails) {
-			return; // Keep WC emails if custom emails disabled
+		// Only disable WC emails if WooNooW system is enabled
+		if (!self::is_enabled()) {
+			return; // Keep WC emails if WooNooW system disabled
 		}
 		
 		// Disable all WooCommerce transactional emails