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/scripts/nomarchy-sudo-keepalive

@@ -0,0 +1,10 @@
+#!/bin/bash
+
+# Prompt for sudo once and keep the credential alive in the background.
+# Source this script so the trap applies to the calling shell:
+#   source nomarchy-sudo-keepalive
+
+sudo -v
+while true; do sudo -n true; sleep 60; done 2>/dev/null &
+SUDO_KEEPALIVE_PID=$!
+trap "kill $SUDO_KEEPALIVE_PID 2>/dev/null" EXIT