fix: prevent listener service from restarting during deployment

Add stopIfChanged and restartIfChanged options to prevent the listener
from being interrupted when nixos-rebuild switch activates a new
configuration that changes the service definition.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

nixos/module.nix

@@ -103,6 +103,11 @@ in
       after = [ "network-online.target" ];
       wants = [ "network-online.target" ];
 
+      # Prevent self-interruption during nixos-rebuild switch
+      # The service will continue running the old version until manually restarted
+      stopIfChanged = false;
+      restartIfChanged = false;
+
       environment = cfg.environment // {
         # Nix needs a writable cache for git flake fetching
         XDG_CACHE_HOME = "/var/cache/homelab-deploy";