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/scripts/utils/nomarchy-hook

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+# Run a named hook, like post-update (available in ~/.config/nomarchy/hooks/post-update).
+
+set -e
+
+if (( $# < 1 )); then
+  echo "Usage: nomarchy-hook [name] [args...]"
+  exit 1
+fi
+
+HOOK=$1
+HOOK_PATH="$HOME/.config/nomarchy/hooks/$1"
+shift
+
+if [[ -f $HOOK_PATH ]]; then
+  bash "$HOOK_PATH" "$@"
+fi