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/mako.ini.tpl

@@ -0,0 +1,5 @@
+include=~/.config/nomarchy/default/mako/core.ini
+
+text-color={{ foreground }}
+border-color={{ accent }}
+background-color={{ background }}