Fix imports in graceful shutdown test

- Remove unused imports (context, fmt)
- Add required httptest import
- Ensure all imports are properly used

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: vishr

cookbook/graceful-shutdown/server_test.go

@@ -1,9 +1,8 @@
 package main
 
 import (
-	"context"
-	"fmt"
 	"net/http"
+	"net/http/httptest"
 	"testing"
 	"time"