Fix updater timer not re-arming after first run

RemainAfterExit=true kept the oneshot 'active' forever, which broke the
timer's OnUnitActiveSec re-arming: the timer fired once (NEXT emptied,
Trigger n/a) and never polled again. Remove it so the service returns to
dead and the 2-min cadence keeps firing.

radiantwave-updater.nix

@@ -38,7 +38,10 @@ in
       wants = [ "network-online.target" ];
       serviceConfig = {
         Type = "oneshot";
-        RemainAfterExit = true;
+        # NOTE: no RemainAfterExit here. Keeping the oneshot "active" after
+        # it finishes breaks the timer's OnUnitActiveSec re-arming, so the
+        # 2-min cadence stops after the first run (NEXT goes empty, Trigger
+        # becomes n/a). Let the service return to dead so the timer refires.
       };
       script = ''
         set -u