Refactor save return type without Either

src/main/scala/app/Main.scala

@@ -9,13 +9,17 @@ import server.Server
 object Main extends IOApp {
   def run(args: List[String]): IO[ExitCode] = {
     for {
+      // TODO run in separate thread
       dbService <- DBService.of
       dataService <- DataService.of(dbService)
+
       fetch <- FetchService.of
       fileFetchScheduler <- FileFetchScheduler.of(dataService, fetch)
       schedulerTask = fileFetchScheduler.run.compile.drain
+
       server <- Server.of(dataService, fetch)
       serverTask = server.run
+
       exitCode <- (serverTask, schedulerTask).parMapN((_, _) => ExitCode.Success)
     } yield exitCode
   }