fix: use log.Fatal for fatal errors

main.go

@@ -1,13 +1,15 @@
 package main
 
 import (
-	"log/slog"
+	"log"
+	"os"
 
 	"github.com/ayn2op/discordo/cmd"
 )
 
 func main() {
 	if err := cmd.Run(); err != nil {
-		slog.Error("failed to run command", "err", err)
+		log.SetOutput(os.Stderr)
+		log.Fatal(err)
 	}
 }