Define imv keys, switch to btop, put stateful data in per-system config

hosts/tower/default.nix

@@ -6,6 +6,7 @@
     ./filesystems
     ./firewall
     ./hardware
+    ./users
     ../../modules/system
   ];
 
@@ -17,4 +18,5 @@
   environment.sessionVariables.NIXOS_OZONE_WL = "1";
 
   networking.hostName = "tower";
+  system.stateVersion = "24.05";
 }