Add fresh install script for ISO installer

- Add installer/fresh-install.sh for installing from live ISO
- Handles disk partitioning, LUKS encryption, filesystem setup
- Generates minimal NixOS config for first boot
- Enable flakes in ISO environment
- Pass installer script content to ISO build via specialArgs

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

iso/default.nix

@@ -5,6 +5,7 @@
   pkgs,
   modulesPath,
   inputs,
+  installerScriptContent,
   ...
 }: {
   imports = [
@@ -68,6 +69,9 @@
 
     # NixOS installation
     nixos-install-tools
+
+    # Nomarchy installer script
+    (writeShellScriptBin "nomarchy-install" installerScriptContent)
   ];
 
   # Auto-login to installer
@@ -80,7 +84,7 @@
     ║                                                           ║
     ║   Welcome to the Nomarchy Installer                       ║
     ║                                                           ║
-    ║   Run 'nomarchy-install' to begin installation            ║
+    ║   Run 'sudo nomarchy-install' to begin installation       ║
     ║                                                           ║
     ║   For more information: https://github.com/blu/nomarchy   ║
     ║                                                           ║
@@ -88,19 +92,6 @@
 
   '';
 
-  # Copy installer script
-  system.activationScripts.installer = ''
-    mkdir -p /usr/local/bin
-    cat > /usr/local/bin/nomarchy-install << 'INSTALLER'
-    #!/usr/bin/env bash
-    # Nomarchy ISO Installer - coming soon
-    echo "ISO installer not yet implemented."
-    echo "Please use the NixOS manual installation process,"
-    echo "then run: nix run github:blu/nomarchy"
-    INSTALLER
-    chmod +x /usr/local/bin/nomarchy-install
-  '';
-
   # User account
   users.users.nixos = {
     isNormalUser = true;
@@ -111,6 +102,9 @@
   # Allow passwordless sudo
   security.sudo.wheelNeedsPassword = false;
 
+  # Enable flakes
+  nix.settings.experimental-features = ["nix-command" "flakes"];
+
   # System state version
   system.stateVersion = "24.11";
 }