♻️ consolidate nix configs

nix/modules/base/nixos.nix

@@ -0,0 +1,37 @@
+{ config, ... }: {
+
+  imports = [ ./common.nix ../monitoring ];
+
+  nix = {
+    gc = {
+      persistent = true;
+      dates = "weekly";
+      options = "--delete-older-than 30d";
+    };
+
+    settings = {
+      auto-optimise-store = true;
+
+      trusted-users = [ "root" "walkah" ];
+    };
+  };
+
+  programs = {
+    mosh.enable = true;
+  };
+
+  services = {
+    openssh.enable = true;
+    tailscale.enable = true;
+  };
+
+  system = {
+    autoUpgrade = {
+      enable = true;
+      flake = "github:walkah/athens#${config.networking.hostName}";
+      dates = "daily";
+      randomizedDelaySec = "5m";
+    };
+    stateVersion = "23.05";
+  };
+}