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-battery-remaining

@@ -0,0 +1,9 @@
+#!/bin/bash
+
+# Returns the battery percentage remaining as an integer.
+# Used by the battery monitor and the Ctrl + Shift + Super + B hotkey.
+
+upower -i $(upower -e | grep BAT) | awk '/percentage/ { 
+    print int($2)
+    exit
+}'