Update keys, add Tailscale to the mailserver

nix-system-configs/modules/system/mail-server.nix

@@ -41,6 +41,9 @@ in {
   ];
 
   config = {
+    # Enable Tailscale for remote access to Traefik dashboard and configuration
+    services.tailscale.enable = true;
+
     local.hostname = "nixos-mailserver";
     local.username = "mailprg";
     local.userDescription = "NixOS PRG Mailing Service";