agent + manager: put claude-code on the harness service PATH

nix/templates/agent-base.nix

@@ -15,6 +15,10 @@
     description = "hive-ag3nt harness";
     wantedBy = [ "multi-user.target" ];
     after = [ "network.target" ];
+    # The harness shells out to `claude` (turn loop + login flow). systemd
+    # units get a minimal PATH by default, so we have to put claude-code on
+    # it explicitly even though it's in environment.systemPackages above.
+    path = [ pkgs.claude-code ];
     serviceConfig = {
       ExecStart = "${pkgs.hyperhive}/bin/hive-ag3nt serve";
       Restart = "on-failure";