fix: remove sshPort from buildMachines (use SSH config instead)

modules/nixos/services/remote-builder.nix

@@ -19,7 +19,7 @@ in {
       port = lib.mkOption {
         type = lib.types.port;
         default = 2424;
-        description = "SSH port on the remote build machine.";
+        description = "SSH port — added via ~root/.ssh/config since nix.buildMachines has no sshPort option.";
       };
       systems = lib.mkOption {
         type = lib.types.listOf lib.types.str;
@@ -50,7 +50,6 @@ in {
     nix.buildMachines = [{
       hostName = cfg.buildMachine.host;
       sshUser = cfg.buildMachine.sshUser;
-      sshPort = cfg.buildMachine.port;
       systems = cfg.buildMachine.systems;
       maxJobs = cfg.buildMachine.maxJobs;
       supportedFeatures = cfg.buildMachine.supportedFeatures;
@@ -60,5 +59,13 @@ in {
       builders-use-substitutes = true
       fallback = true
     '';
+
+    # SSH config for the remote builder (since nix.buildMachines has no port option)
+    programs.ssh.extraConfig = ''
+      Host ${cfg.buildMachine.host}
+        HostName ${cfg.buildMachine.host}
+        Port ${toString cfg.buildMachine.port}
+        User ${cfg.buildMachine.sshUser}
+    '';
   };
 }