fix(docs): improve layout consistency for documentation cards

- Wrap API Server card in a CardGrid component
- Add spacing above the card for better visual separation
- Close the CardGrid before the "Choose Your Path" section to avoid layout issues

Author: fulleni

src/content/docs/index.mdx

@@ -75,6 +75,8 @@ Welcome to the Flutter News App Full Source Code Toolkit. This is more than just
 			</a>
 		</div>
 	</Card>
+</CardGrid>
+<div style={{ marginTop: '1rem' }}>
 	<Card title="API Server" icon="cloud">
 		A high-performance backend built with Dart Frog, providing robust APIs for
 		authentication, data management, and remote configuration.
@@ -94,7 +96,7 @@ Welcome to the Flutter News App Full Source Code Toolkit. This is more than just
 			</a>
 		</div>
 	</Card>
-</CardGrid>
+</div>
 
 ## Choose Your Path