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/services.nix

@@ -33,6 +33,6 @@
         InterceptUnknown = true;
         ProcMonitorMethod = "ebpf";
       };
-      scx.scheduler = "scx_rustland";
+      # scx.scheduler = "scx_rustland";
     };
 }