scripts: add create-host tool for automated host configuration generation

Implements Phase 2 of the automated deployment pipeline.

This commit adds a Python CLI tool that automates the creation of NixOS host
configurations, eliminating manual boilerplate and reducing errors.

Features:
- Python CLI using typer framework with rich terminal UI
- Comprehensive validation (hostname format/uniqueness, IP subnet/uniqueness)
- Jinja2 templates for NixOS configurations
- Automatic updates to flake.nix and terraform/vms.tf
- Support for both static IP and DHCP configurations
- Dry-run mode for safe previews
- Packaged as Nix derivation and added to devShell

Usage:
  create-host --hostname myhost --ip 10.69.13.50/24

The tool generates:
- hosts/<hostname>/default.nix
- hosts/<hostname>/configuration.nix
- Updates flake.nix with new nixosConfigurations entry
- Updates terraform/vms.tf with new VM definition

All generated configurations include full system imports (monitoring, SOPS,
autoupgrade, etc.) and are validated with nix flake check and tofu validate.

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

flake.nix

@@ -335,6 +335,12 @@
           ];
         };
       };
+      packages = forAllSystems (
+        { pkgs }:
+        {
+          create-host = pkgs.callPackage ./scripts/create-host { };
+        }
+      );
       devShells = forAllSystems (
         { pkgs }:
         {
@@ -342,7 +348,7 @@
             packages = with pkgs; [
               ansible
               opentofu
-              python3
+              (pkgs.callPackage ./scripts/create-host { })
             ];
           };
         }