refactor: archive old features directory to features.old

The new profile-based structure (home/base, home/desktop, home/server,
home/profiles/, home/coding) is fully operational and imported via
home/lib/mkHomeConfig. The legacy home/features directory is no longer
referenced anywhere in the configuration.

Archived rather than deleted to preserve history for reference.

home/features.old/desktop/fonts.nix

@@ -0,0 +1,24 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+with lib; let
+  cfg = config.features.desktop.fonts;
+in {
+  options.features.desktop.fonts.enable =
+    mkEnableOption "install additional fonts for desktop apps";
+
+  config = mkIf cfg.enable {
+    home.packages = with pkgs; [
+      fira-code
+      fira-code-symbols
+      nerd-fonts.fira-code
+      nerd-fonts.jetbrains-mono
+      font-manager
+      font-awesome_5
+      noto-fonts
+    ];
+  };
+}