greetd: terminal.vt = 2

when vt = 1 (default), some dmesg/systemd log messages spammed and overrided the tuigreet tui.

etcnixos/common.nix

@@ -40,6 +40,7 @@
         command = "${lib.getExe pkgs.tuigreet} --time --cmd niri-session";
         user = username;
       };
+      terminal.vt = lib.mkForce 2;
     };
   };