now using flake-parts; refactored nixosConfigurations; using hm standalone

hosts/modules/server/boot.nix

@@ -0,0 +1,5 @@
+{ pkgs, ... }:
+
+{
+  boot.kernelPackages = pkgs.linuxPackages_hardened;
+}

hosts/modules/server/nix.nix

@@ -0,0 +1,13 @@
+{ inputs, ... }:
+
+{
+  environment.etc."channels/nixpkgs".source = inputs.nixpkgs-stable.outPath;
+
+  nix = {
+    registry.nixpkgs.flake = inputs.nixpkgs-stable;
+    nixPath = [
+      "nixpkgs=/etc/channels/nixpkgs"
+      "/nix/var/nix/profiles/per-user/root/channels"
+    ];
+  };
+}

hosts/modules/server/tailscale.nix

@@ -0,0 +1,13 @@
+{ ... }:
+
+{
+  services.tailscale = {
+    extraSetFlags = [ "--advertise-exit-node" ];
+    useRoutingFeatures = "server";
+  };
+
+  boot.kernel.sysctl = {
+    "net.ipv4.ip_forward" = 1;
+    "net.ipv6.conf.all.forwarding" = 1;
+  };
+}