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

BACKEND_WIRING_COMPLETE.md

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+# Backend Wiring Complete ✅
+
+## Summary
+All notification system components are fully wired and functional.
+
+## What's Wired
+
+### 1. Template System ✅
+- Save/Get templates via API
+- EmailRenderer uses templates
+- Variables replaced automatically
+- Markdown parsed (cards, buttons, images)
+
+### 2. Channel Toggles ✅
+- Frontend toggles saved to database
+- NotificationManager checks before sending
+- Email: `woonoow_email_notifications_enabled`
+- Push: `woonoow_push_notifications_enabled`
+
+### 3. Event Toggles ✅
+- Per-event channel settings saved
+- Stored in `woonoow_notification_settings`
+- Checked before sending notifications
+
+### 4. Global System Toggle ✅
+- NEW: Switch between WooNooW and WooCommerce
+- API: `GET/POST /notifications/system-mode`
+- Stored in: `woonoow_notification_system_mode`
+- EmailManager respects this setting
+- NotificationManager checks before sending
+
+### 5. Email Customization ✅
+- Colors, logo, branding saved
+- EmailRenderer applies customization
+- Stored in: `woonoow_email_settings`
+
+### 6. Push Settings ✅
+- Icon, badge, sound settings
+- PushNotificationHandler applies settings
+
+## Notification Flow
+
+```
+Event → EmailManager → Check System Mode → Check Channel Toggle
+→ Check Event Toggle → EmailRenderer → Get Template → Replace Variables
+→ Parse Markdown → Apply Branding → wp_mail() → Sent ✅
+```
+
+## Key Files Modified
+- `NotificationsController.php`: Added system-mode endpoints
+- `NotificationManager.php`: Added system mode check
+- `EmailManager.php`: Added is_enabled() check
+
+## Testing
+All settings are now saved and applied when sending notifications.