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/theme.nix

@@ -0,0 +1,22 @@
+{
+  config,
+  pkgs,
+  ...
+}: {
+  qt = {
+    enable = true;
+    platformTheme.name = "gtk";
+  };
+  gtk = {
+    enable = true;
+    theme = {
+      name = "Dracula";
+      package = pkgs.dracula-theme;
+    };
+    iconTheme = {
+      name = "Dracula";
+      package = pkgs.dracula-icon-theme;
+    };
+    gtk4.theme = config.gtk.theme;
+  };
+}