docs: add explanation of how the toolkit components fit together

- Added a new section "How the Toolkit Fits Together" to clarify the relationship between API Server, Mobile Client, and Web Dashboard
- Explained the separation of concerns and its benefits for platform management and mobile updates

Author: fulleni

src/content/docs/index.mdx

@@ -100,6 +100,12 @@ Welcome to the Flutter News App Full Source Code Toolkit. This is more than just
 	</Card>
 </div>
 
+## How the Toolkit Fits Together
+
+The **API Server** is the central brain. Both the **Mobile Client** and the **Web Dashboard** communicate with it to fetch data, authenticate users, and retrieve configuration. The **Web Dashboard** is used to populate the content that the **Mobile Client** displays.
+
+This separation of concerns makes the toolkit robust and flexible. You can manage your entire platform from the web and deliver updates to your mobile users instantly.
+
 ## Get Started: Try, Evaluate, and Launch
 
 This toolkit is source-available, allowing you to explore the code and ensure it meets your standards before making a commitment.