feat: Implement push notification settings backend and UI

## ✅ Push Notification Settings - Fully Functional

### Backend (PHP)

**PushNotificationHandler Updates:**
- Added `SETTINGS_KEY` constant
- `ensure_default_settings()` - Initialize defaults
- `get_default_settings()` - Return default config
- `get_settings()` - Fetch current settings
- `update_settings()` - Save settings

**Default Settings:**
```php
[
  'use_logo' => true,
  'use_product_images' => true,
  'use_gravatar' => false,
  'click_action' => '/wp-admin/admin.php?page=woonoow#/orders',
  'require_interaction' => false,
  'silent' => false,
]
```

**NotificationsController:**
- `GET /notifications/push/settings` - Fetch settings
- `POST /notifications/push/settings` - Update settings
- Permission-protected endpoints

### Frontend (React)

**ChannelConfig Component:**
- Fetches push settings on open
- Real-time state management
- Connected switches and inputs
- Save mutation with loading state
- Toast notifications for success/error
- Disabled state during save

**Settings Available:**
1. **Branding**
   - Use Store Logo
   - Use Product Images
   - Use Customer Gravatar

2. **Behavior**
   - Click Action URL (input)
   - Require Interaction
   - Silent Notifications

### Features

✅ **Backend Storage** - Settings saved in wp_options
✅ **REST API** - GET and POST endpoints
✅ **Frontend UI** - Full CRUD interface
✅ **State Management** - React Query integration
✅ **Loading States** - Skeleton and button states
✅ **Error Handling** - Toast notifications
✅ **Default Values** - Sensible defaults

---

**Next: Email channel toggle** 📧

includes/Core/Notifications/PushNotificationHandler.php

@@ -21,12 +21,80 @@ class PushNotificationHandler {
 	 */
 	const VAPID_KEYS_KEY = 'woonoow_push_vapid_keys';
 	
+	/**
+	 * Option key for push settings
+	 */
+	const SETTINGS_KEY = 'woonoow_push_settings';
+	
 	/**
 	 * Initialize push notifications
 	 */
 	public static function init() {
 		// Generate VAPID keys if not exists
 		self::ensure_vapid_keys();
+		
+		// Ensure default settings exist
+		self::ensure_default_settings();
+	}
+	
+	/**
+	 * Ensure default push settings exist
+	 * 
+	 * @return array
+	 */
+	public static function ensure_default_settings() {
+		$settings = get_option(self::SETTINGS_KEY);
+		
+		if (!$settings) {
+			$settings = self::get_default_settings();
+			update_option(self::SETTINGS_KEY, $settings);
+		}
+		
+		return $settings;
+	}
+	
+	/**
+	 * Get default push settings
+	 * 
+	 * @return array
+	 */
+	public static function get_default_settings() {
+		return [
+			'use_logo' => true,
+			'use_product_images' => true,
+			'use_gravatar' => false,
+			'click_action' => '/wp-admin/admin.php?page=woonoow#/orders',
+			'require_interaction' => false,
+			'silent' => false,
+		];
+	}
+	
+	/**
+	 * Get push settings
+	 * 
+	 * @return array
+	 */
+	public static function get_settings() {
+		$settings = get_option(self::SETTINGS_KEY);
+		
+		if (!$settings) {
+			$settings = self::get_default_settings();
+		}
+		
+		return $settings;
+	}
+	
+	/**
+	 * Update push settings
+	 * 
+	 * @param array $settings
+	 * @return bool
+	 */
+	public static function update_settings($settings) {
+		$current = self::get_settings();
+		$updated = array_merge($current, $settings);
+		
+		return update_option(self::SETTINGS_KEY, $updated);
 	}
 	
 	/**