fix(nixos): address Nix review findings

Render Palworld secrets through its documented settings file and remove stale RCON configuration.

Harden generated commands, centralize shared modules, and codify the reviewed Nix conventions.

configs/nixos/hosts/pikachu/default.nix

@@ -60,7 +60,6 @@
     serverName = "Tracion";
     autoStart = false;
     adminPasswordSecret = "services/game-servers/admin/password";
-    publicIP = config.guests.palworld.address;
     reverseProxy = {
       enable = true;
       route = {

configs/nixos/hosts/zeus/default.nix

@@ -1,6 +1,5 @@
 {
   config,
-  lib,
   ...
 }:
 # zeus — Ryzen desktop with AMD graphics.
@@ -8,9 +7,9 @@
 # `fileSystems` are derived from it, none declared here.
 {
   imports = [
+    ./hardware-configuration.nix
     ./disk.nix
-  ]
-  ++ lib.optional (builtins.pathExists ./hardware-configuration.nix) ./hardware-configuration.nix;
+  ];
 
   nixpkgs.hostPlatform = "x86_64-linux";