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

themes/templates/hyprland.conf.tpl

@@ -0,0 +1,9 @@
+$activeBorderColor = rgb({{ accent_strip }})
+
+general {
+    col.active_border = $activeBorderColor
+}
+
+group {
+    col.border_active = $activeBorderColor
+}