chore: remove features.old archive and format all files

- Delete home/features.old/ (archived old flat feature modules)
- All content migrated to new profile-based structure
- Run alejandra formatter over 13 changed files
- nix flake check passes cleanly

hosts/m3-hermes/hardware-configuration.nix

@@ -1,7 +1,13 @@
 # Do not modify this file!  It was generated by 'nixos-generate-config'
 # and may be overwritten by future invocations.  Please make changes
 # to configuration.nix instead.
-{config, lib, pkgs, modulesPath, ...}: {
+{
+  config,
+  lib,
+  pkgs,
+  modulesPath,
+  ...
+}: {
   imports = [
     (modulesPath + "/profiles/qemu-guest.nix")
   ];