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

features/apps/scripts/nomarchy-restart-app

@@ -0,0 +1,7 @@
+#!/bin/bash
+
+# Restart an application by killing it and relaunching via uwsm.
+# Usage: nomarchy-restart-app <application-name> [application-args...]
+
+pkill -x $1
+setsid uwsm-app -- "$@" >/dev/null 2>&1 &