feat(jeeves): share one system closure across builders

Reuse a single NixOS container build for all runners while preserving
unique runtime hostnames and existing Gitea registrations.

systems/jeeves/runners/nix_builder.nix

@@ -184,93 +184,6 @@ in
             isReadOnly = false;
           };
         };
-        config =
-          {
-            config,
-            pkgs,
-            lib,
-            ...
-          }:
-          {
-            networking = {
-              useDHCP = lib.mkDefault true;
-              interfaces.eth0.useDHCP = true;
-              # Ensure containers don't inherit the host's stub resolver (127.0.0.53) which was causing issues
-              useHostResolvConf = false;
-            };
-            nix.settings = {
-              trusted-substituters = [
-                "https://cache.nixos.org"
-                "https://cache.tmmworkshop.com"
-                "https://nix-community.cachix.org"
-              ];
-              substituters = [
-                "https://cache.nixos.org/?priority=2&want-mass-query=true"
-                "https://cache.tmmworkshop.com/?priority=2&want-mass-query=true"
-                "https://nix-community.cachix.org/?priority=10&want-mass-query=true"
-              ];
-              trusted-public-keys = [
-                "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
-                "cache.tmmworkshop.com:jHffkpgbmEdstQPoihJPYW9TQe6jnQbWR2LqkNGV3iA="
-                "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
-              ];
-              experimental-features = [
-                "flakes"
-                "nix-command"
-              ];
-              sandbox = true;
-              allowed-users = [ "gitea-runner" ];
-              trusted-users = [
-                "root"
-                "gitea-runner"
-              ];
-            };
-            nixpkgs = {
-              overlays = builtins.attrValues outputs.overlays;
-              config.allowUnfree = true;
-            };
-            users = {
-              users.${runnerUsername} = {
-                isSystemUser = true;
-                group = runnerUsername;
-                uid = runnerUserid;
-              };
-              groups.${runnerUsername}.gid = runnerUserid;
-            };
-            services.gitea-actions-runner.instances.${name} = {
-              enable = true;
-              name = "jeeves-${name}";
-              url = "http://192.168.99.14:6443/";
-              labels = [
-                "self-hosted:host"
-                "nixos:host"
-              ];
-              tokenFile = "/run/secrets/gitea-runners/registration-token";
-              hostPackages = with pkgs; [
-                bash
-                coreutils
-                curl
-                gawk
-                gitMinimal
-                gnused
-                my_python
-                nix
-                nixfmt
-                nixos-rebuild
-                nodejs
-                treefmt
-                wget
-              ];
-            };
-            systemd.services."gitea-runner-${utils.escapeSystemdPath name}" = {
-              serviceConfig = {
-                DynamicUser = mkForce false;
-                User = mkForce runnerUsername;
-                Group = mkForce runnerUsername;
-              };
-            };
-            system.stateVersion = "24.05";
-          };
       }
     ) cfg.containers;