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

modules/system/services/general/displaymanager/default.nix

@@ -0,0 +1,14 @@
+{ config, pkgs, ... }:
+{
+  services.greetd = {
+    enable = config.system.desktop.enable;
+    restart = true;
+    settings = {
+      terminal = {
+        vt = 2;
+        switch = true;
+      };
+      default_session.command = "${pkgs.greetd.tuigreet}/bin/tuigreet";
+    };
+  };
+}