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/host.nix

@@ -0,0 +1,29 @@
+{
+  config,
+  lib,
+  ...
+}: let
+  inherit (lib) mkOption types;
+  cfg = config.unexplrd.host;
+in {
+  options.unexplrd.host = {
+    name = mkOption {
+      type = types.str;
+    };
+    id = mkOption {
+      type = types.strMatching "[a-z0-9]{8}";
+    };
+    stateVersion = mkOption {
+      type = types.strMatching ''[0-9]{2}\.[0-9]{2}'';
+    };
+    type = mkOption {
+      type = types.enum ["laptop" "server" "workstation"];
+    };
+  };
+
+  config = {
+    system.stateVersion = cfg.stateVersion;
+    networking.hostName = cfg.name;
+    networking.hostId = cfg.id;
+  };
+}