Enable u2f auth

hosts/fenixpc/fenix.nix

@@ -1,6 +1,5 @@
 {
   pkgs,
-  pkgsStable,
   lib,
   config,
   osConfig,

roles/desktop.nix

@@ -82,6 +82,12 @@ in
     };
 
     pam = {
+      u2f = {
+        enable = true;
+        settings = {
+          cue = true;
+        };
+      };
       yubico.enable = true;
       yubico.mode = "challenge-response";
     };