docs(README): update backend API and content dashboard links

- Remove Flutter News App prefix from repository links
- Separate backend API and content dashboard into individual links
- Remove "dart frog" from backend API description for consistency

Author: fulleni

README.md

@@ -5,7 +5,7 @@
 [![style: very good analysis](https://img.shields.io/badge/style-very_good_analysis-B22C89.svg)](https://pub.dev/packages/very_good_analysis)
 [![License: PolyForm Free Trial](https://img.shields.io/badge/License-PolyForm%20Free%20Trial-blue)](https://polyformproject.org/licenses/free-trial/1.0.0)
 
-This is a complete and fully-functional Flutter news application. It gives you everything you need to launch your own news app on the App Store and Google Play, right out of the box. It is a key component of the [**Flutter News App - Full Source Code Toolkit**](https://github.com/flutter-news-app-full-source-code), an ecosystem that also includes a [Dart Frog backend API](https://github.com/flutter-news-app-full-source-code/flutter-news-app-api-server-full-source-code) and a [web-based content dashboard](https://github.com/flutter-news-app-full-source-code/flutter-news-app-web-dashboard-full-source-code).
+This is a complete and fully-functional Flutter news application. It gives you everything you need to launch your own news app on the App Store and Google Play, right out of the box. It is a key component of the [**Flutter News App - Full Source Code Toolkit**](https://github.com/flutter-news-app-full-source-code), an ecosystem that also includes a dart frog [backend API](https://github.com/flutter-news-app-full-source-code/flutter-news-app-api-server-full-source-code) and a web-based [content dashboard](https://github.com/flutter-news-app-full-source-code/flutter-news-app-web-dashboard-full-source-code).
 
 ## ⭐ Everything You Get, Ready to Go