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-install

@@ -0,0 +1,33 @@
+#!/bin/bash
+
+# nomarchy-theme-install: Install a new theme from a git repo for Nomarchy
+# Usage: nomarchy-theme-install <git-repo-url>
+
+if [[ -z $1 ]]; then
+  echo -e "\e[32mSee https://manuals.omamix.org/2/the-nomarchy-manual/90/extra-themes\n\e[0m"
+  REPO_URL=$(gum input --placeholder="Git repo URL for theme" --header="")
+else
+  REPO_URL="$1"
+fi
+
+if [[ -z $REPO_URL ]]; then
+  exit 1
+fi
+
+THEMES_DIR="$HOME/.config/nomarchy/themes"
+THEME_NAME=$(basename "$REPO_URL" .git | sed -E 's/^nomarchy-//; s/-theme$//')
+THEME_PATH="$THEMES_DIR/$THEME_NAME"
+
+# Remove existing theme if present
+if [[ -d $THEME_PATH ]]; then
+  rm -rf "$THEME_PATH"
+fi
+
+# Clone the repo directly to ~/.config/nomarchy/themes
+if ! git clone "$REPO_URL" "$THEME_PATH"; then
+  echo "Error: Failed to clone theme repo."
+  exit 1
+fi
+
+# Apply the new theme with nomarchy-theme-set
+nomarchy-theme-set $THEME_NAME