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-tz-select

@@ -0,0 +1,12 @@
+#!/usr/bin/env bash
+
+# Select system timezone declaratively for Nomarchy NixOS.
+
+STATE_FILE="/etc/nixos/state.json"
+
+timezone=$(timedatectl list-timezones | gum filter --height 20 --header "Set timezone") || exit 1
+
+sudo jq --arg tz "$timezone" '.timezone = $tz' "$STATE_FILE" > /tmp/state.json && sudo mv /tmp/state.json "$STATE_FILE"
+
+echo "Timezone is now set to $timezone. Applying changes..."
+sudo sys-update