feat: Flake | revamp entire flake (#1)

Reviewed-on: #1

hosts/common/optional/yubikey.nix

@@ -0,0 +1,22 @@
+{
+  pkgs,
+  ...
+}:
+
+{
+  # yubikey login / sudo
+  security.pam = {
+    u2f = {
+      enable = true;
+      settings.cue = true;
+    };
+    services = {
+      login.u2fAuth = true;
+      sudo.u2fAuth = true;
+    };
+  };
+
+  environment.systemPackages = with pkgs; [
+    yubikey-manager
+  ];
+}