Nix Config Rewrite

nix config rewrite Rewrote the entire nix-config. The previous version worked but was held together with optimism and duct tape — values scattered across files, custom cfgLib/specialArgs patterns that fought the module system. Replaced all of it with proper Nix modules using modules/options.nix for configuration. Switched from ragenix to sops-nix for secrets management. Moved desktop config from GNOME to KDE Plasma with plasma-manager. Tightened the macmini and server configs. The result: nix flake check passes, the config is leaner and more declarative, and changing a setting no longer requires hunting through multiple files. Repo version bumped to v0.3.1.