Split shared host config into dedicated modules

- Add shared modules for boot, hardware, networking, input, and host defaults
- Move host-specific TOML flags to new option namespaces
- Update SSH and service defaults for the new layout

modules/nixos/shared/module/lanzaboote.nix

@@ -8,7 +8,7 @@
   ];
   boot = {
     lanzaboote = {
-      enable = config.unexplrd.config.secureBoot;
+      enable = config.unexplrd.boot.secureBoot.enable;
       pkiBundle = "/var/lib/sbctl";
     };
   };