refactor: implement component-based architecture for enhanced maintainability

- Reorganize directory structure into core/, features/, and themes/
- Colocate application Nix logic, configs, scripts, and theme overrides
- Implement 'Inversion of Control' for theming: apps now pull theme-specific layouts
- Update flake.nix and shared library paths to match the new structure
- Document the new Feature-Centric architecture in README.md

core/home/security.nix

@@ -0,0 +1,22 @@
+{ pkgs, ... }:
+
+{
+  systemd.user.services.polkit-gnome-authentication-agent-1 = {
+    Unit = {
+      Description = "Polkit GNOME Authentication Agent";
+      After = [ "graphical-session.target" ];
+      PartOf = [ "graphical-session.target" ];
+    };
+
+    Service = {
+      ExecStart = "${pkgs.polkit_gnome}/libexec/polkit-gnome-authentication-agent-1";
+      Restart = "on-failure";
+      RestartSec = 1;
+      TimeoutStopSec = 10;
+    };
+
+    Install = {
+      WantedBy = [ "graphical-session.target" ];
+    };
+  };
+}