Update README and SDKClient to improve instructions and ensure proper shutdown

Author: roryp

04-PracticalSamples/calculator/README.md

@@ -250,7 +250,7 @@ export GITHUB_TOKEN=your_github_token_here
 Start the server:
 ```bash
 cd 04-PracticalSamples/calculator
-mvn spring-boot:run
+mvn clean spring-boot:run
 ```
 
 The server will start on `http://localhost:8080`. You should see:

04-PracticalSamples/calculator/src/test/java/com/microsoft/mcp/sample/client/SDKClient.java

@@ -96,5 +96,14 @@ public void run() {
 
 		// Clean up the connection
 		client.closeGracefully();
+
+		// Give threads time to shut down properly before exiting
+		try {
+			Thread.sleep(100);
+		} catch (InterruptedException e) {
+			Thread.currentThread().interrupt();
+		}
+
+		System.exit(0);
 	}
 }