harness-base: wrap config attributes after introducing options

mixing options.* with bare config-level attributes (boot.*, environment.*, etc.) at the same level isn't supported once the module declares any options — nix needs them under an explicit 'config = { ... }' block. error from the host: 'unsupported attribute boot. caused by introducing top-level options'. wrap accordingly.

nix/templates/harness-base.nix

@@ -59,6 +59,7 @@
     '';
   };
 
+  config = {
     environment.etc."hyperhive/extra-mcp.json".text =
       builtins.toJSON config.hyperhive.extraMcpServers;
 
@@ -100,4 +101,5 @@
     environment.variables.SHELL = "${pkgs.bashInteractive}/bin/bash";
 
     system.stateVersion = "25.11";
+  };
 }