Fixes duplicate module declaration error by importing terranix
flakeModule once at the top level instead of in each config file.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
Each terranix configuration now exports its own flake output as a
self-contained module. Flattened directory structure and removed
centralized terranixConfigurations.nix in favor of import-tree.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
