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/engine/scripts/nomarchy-theme-bg-set

@@ -0,0 +1,18 @@
+#!/bin/bash
+
+# Sets the specified image as the current background
+
+if [[ -z $1 ]]; then
+  echo "Usage: nomarchy-theme-bg-set <path-to-image>" >&2
+  exit 1
+fi
+
+BACKGROUND="$1"
+CURRENT_BACKGROUND_LINK="$HOME/.config/nomarchy/current/background"
+
+# Create symlink to the new background
+ln -nsf "$BACKGROUND" "$CURRENT_BACKGROUND_LINK"
+
+# Kill existing swaybg and start new one
+pkill -x swaybg
+setsid uwsm-app -- swaybg -i "$CURRENT_BACKGROUND_LINK" -m fill >/dev/null 2>&1 &