restructure

- users/rin/default.nix -> users/rin.nix
- users/rin/home.nix +-> users/rin.nix
- users/rin/*.nix -> modules/user/*.nix
- users/rin/scripts/ -> scripts/
- hosts/winter/default.nix -> hosts/winter.nix
- hosts/winter/*.nix -> modules/system/*.nix

- modules are dynamically imported as sets for system and user

modules/system/security.nix

@@ -0,0 +1,24 @@
+{ config, pkgs, ... }: {
+  networking.firewall.enable = false;
+
+  services.openssh = {
+    enable = true;
+    permitRootLogin = "no";
+    passwordAuthentication = false;
+  };
+
+  security = {
+    polkit.enable = true;
+    sudo.enable = false;
+    doas = {
+      enable = true;
+      extraRules = [
+        {
+          groups = ["wheel"];
+          keepEnv = true;
+          persist = true;
+        }
+      ];
+    };
+  };
+}