Major config overhaul: use custom modules, setup for multi-host config, and less boilerplate

modules/system/bluetooth/default.nix

@@ -0,0 +1,16 @@
+{ lib, config, ... }:
+
+let
+  cfg = config.systemSettings.bluetooth;
+in {
+  options = {
+    systemSettings.bluetooth = {
+      enable = lib.mkEnableOption "Enable bluetooth";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    hardware.bluetooth.enable = true;
+    services.blueman.enable = true;
+  };
+}