Also close database gracefully

server/main.go

@@ -114,5 +114,9 @@ func main() {
 		log.Fatalf("Server shutdown failed: %v", err)
 	}
 
+	if err := server.DB.Close(); err != nil {
+		log.Fatalf("Database close failed: %v", err)
+	}
+
 	log.Println("Server stopped")
 }