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/Api/NotificationsController.php

@@ -199,6 +199,24 @@ class NotificationsController {
 				'permission_callback' => [$this, 'check_permission'],
 			],
 		]);
+		
+		// GET /woonoow/v1/notifications/system-mode
+		register_rest_route($this->namespace, '/' . $this->rest_base . '/system-mode', [
+			[
+				'methods' => 'GET',
+				'callback' => [$this, 'get_system_mode'],
+				'permission_callback' => [$this, 'check_permission'],
+			],
+		]);
+		
+		// POST /woonoow/v1/notifications/system-mode
+		register_rest_route($this->namespace, '/' . $this->rest_base . '/system-mode', [
+			[
+				'methods' => 'POST',
+				'callback' => [$this, 'set_system_mode'],
+				'permission_callback' => [$this, 'check_permission'],
+			],
+		]);
 	}
 	
 	/**
@@ -799,4 +817,56 @@ class NotificationsController {
 		
 		return $sanitized;
 	}
+	
+	/**
+	 * Get notification system mode
+	 * 
+	 * @param WP_REST_Request $request Request object
+	 * @return WP_REST_Response
+	 */
+	public function get_system_mode(WP_REST_Request $request) {
+		$mode = get_option('woonoow_notification_system_mode', 'woonoow');
+		
+		return new WP_REST_Response([
+			'mode' => $mode,
+			'available_modes' => [
+				'woonoow' => __('WooNooW Notifications', 'woonoow'),
+				'woocommerce' => __('WooCommerce Default Emails', 'woonoow'),
+			],
+		], 200);
+	}
+	
+	/**
+	 * Set notification system mode
+	 * 
+	 * @param WP_REST_Request $request Request object
+	 * @return WP_REST_Response|WP_Error
+	 */
+	public function set_system_mode(WP_REST_Request $request) {
+		$params = $request->get_json_params();
+		$mode = isset($params['mode']) ? $params['mode'] : null;
+		
+		if (!in_array($mode, ['woonoow', 'woocommerce'])) {
+			return new WP_Error(
+				'invalid_mode',
+				__('Invalid notification system mode', 'woonoow'),
+				['status' => 400]
+			);
+		}
+		
+		// Update the mode
+		update_option('woonoow_notification_system_mode', $mode);
+		
+		// Trigger action for other systems to react
+		do_action('woonoow_notification_system_mode_changed', $mode);
+		
+		return new WP_REST_Response([
+			'success' => true,
+			'mode' => $mode,
+			'message' => sprintf(
+				__('Notification system switched to %s', 'woonoow'),
+				$mode === 'woonoow' ? __('WooNooW', 'woonoow') : __('WooCommerce', 'woonoow')
+			),
+		], 200);
+	}
 }