ServiceWorker registration fails in Facebook/Instagram in-app browser on iOS

When using the Firebase Messaging service with Angular 19.1.4 in the Facebook/Instagram in-app browser on iOS devices, the following error occurs:
```typescript
TypeError: undefined is not an object (evaluating 'navigator.serviceWorker.addEventListener')
```

### Environment
- **Platform**: iOS
- **Browser**: Facebook/Instagram in-app browser
- **Framework**: Angular 19.1.4
- **Dependencies**:
- @angular/core: 19.1.4
- @angular/common: 19.1.4
- @angular/platform-browser: 19.1.4
- **Service**: Firebase Cloud Messaging

### Technical Details
The error occurs during the messaging service initialization when attempting to add an event listener to the ServiceWorker. The specific line causing the issue is:
```typescript
navigator.serviceWorker.addEventListener('message', e => messageEventListener(messaging as MessagingService, e));
```

### Root Cause
The Facebook/Instagram in-app browser on iOS does not support or properly expose the ServiceWorker API, causing `navigator.serviceWorker` to be undefined. This issue persists even with the latest Angular 19 framework.

### Impact
- Firebase Cloud Messaging service initialization fails
- Push notifications cannot be registered or received
- Affects only users accessing the Angular 19 application through Facebook/Instagram in-app browser on iOS devices

Start at the messaging-service initialization call shown in the issue and reproduce it in Facebook/Instagram's iOS in-app browser. Trace how navigator.serviceWorker is accessed; done means initialization no longer throws when the API is unavailable, with push behavior verified where supported.

Written by the indexing model from the issue text.