nixos: profiles: move from top-level

My profiles are actually just "special" NixOS modules in that they
orchestrate settings that usually span the NixOS/home-manager boundary,
or otherwise set up configurations from multiple modules at once.

modules/nixos/profiles/laptop/default.nix

@@ -0,0 +1,23 @@
+{ config, lib, ... }:
+let
+  cfg = config.my.profiles.laptop;
+in
+{
+  options.my.profiles.laptop = with lib; {
+    enable = mkEnableOption "laptop profile";
+  };
+
+  config = lib.mkIf cfg.enable {
+    # Enable touchpad support
+    services.xserver.libinput.enable = true;
+
+    # Enable TLP power management
+    my.services.tlp.enable = true;
+
+    # Enable upower power management
+    my.hardware.upower.enable = true;
+
+    # Enable battery notifications
+    my.home.power-alert.enable = true;
+  };
+}