docs(mobile-client): add introduction documentation

- Overview of the Flutter News App Mobile Client
- Core technologies used (Flutter, Bloc, go_router)
- Key features highlighted with card grid
- Getting started guide link included

Author: fulleni

src/content/docs/mobile-client/introduction.mdx

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+---
+title: Introduction
+description: An overview of the Flutter News App Mobile Client.
+---
+
+import { Card, CardGrid } from '@astrojs/starlight/components';
+
+Welcome to the documentation for the Flutter News App Mobile Client, a key component of the Flutter News App Toolkit. This application is a feature-rich, cross-platform mobile app built with Flutter, designed to deliver a seamless and engaging news consumption experience to your users on both iOS and Android.
+
+## Core Technologies
+
+The mobile client is built on a modern, scalable, and maintainable tech stack, ensuring a high-quality foundation for your product.
+
+- **Framework**: [Flutter](https://flutter.dev/) for building beautiful, natively compiled applications for mobile from a single codebase.
+- **State Management**: [Bloc](https://bloclibrary.dev/) for predictable and testable state management, separating business logic from the UI.
+- **Routing**: [go_router](https://pub.dev/packages/go_router) for a declarative, URL-based navigation system that is robust and easy to manage.
+- **Architecture**: Follows the layered architecture principles outlined in the Core Philosophy, ensuring a clean separation of concerns between the UI, business logic, and data layers.
+
+## Key Features
+
+The mobile client comes packed with features designed to provide a comprehensive user experience.
+
+<CardGrid>
+	<Card title="Dynamic Headlines Feed" icon="newspaper">
+		A customizable news feed that supports pagination, pull-to-refresh, and dynamic content injection for ads and user engagement prompts.
+	</Card>
+	<Card title="Advanced Search" icon="search">
+		Users can search for headlines, topics, or sources, with results displayed in a clear and intuitive interface.
+	</Card>
+	<Card title="User Personalization" icon="user">
+		Authenticated users can personalize their experience by following topics and sources, and saving articles to read later.
+	</Card>
+	<Card title="Comprehensive Settings" icon="settings">
+		A detailed settings module allows users to customize the app's appearance, theme, font size, language, and feed display preferences.
+	</Card>
+</CardGrid>
+
+## Getting Started
+
+To get the mobile client up and running on your local machine, head over to our setup guide.
+
+- **[Local Setup Guide](./getting-started/local-setup)**