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/system/bluetooth.nix

@@ -0,0 +1,7 @@
+{ config, pkgs, lib, ... }:
+
+{
+  hardware.bluetooth.enable = lib.mkDefault true;
+  hardware.bluetooth.powerOnBoot = lib.mkDefault true;
+  services.blueman.enable = lib.mkDefault true;
+}