feat: server-side remote builder config (lazyworkhorse dispatches aarch64 to uConsole)

Server only — uConsole-side config will be added in uconsole-cm5-incremental branch.
Includes reusable module, builder system user, and SSH key placeholder.

hosts/lazyworkhorse/configuration.nix

@@ -573,5 +573,23 @@
   # For more information, see `man configuration.nix` or https://nixos.org/manual/nixos/stable/options#opt-system.stateVersion .
   system.stateVersion = "25.05"; # Did you read the comment?
 
+
+  # ============================================================
+  # Remote builder — dispatches aarch64-linux builds to uConsole
+  # ============================================================
+  services.remoteBuilder = {
+    enable = true;
+    machines = [
+      {
+        hostName = "192.168.1.120";
+        port = 22;
+        sshUser = "builder";
+        sshKey = "/etc/ssh/builder_key";
+        systems = [ "aarch64-linux" ];
+        maxJobs = 4;
+      }
+    ];
+  };
+
 }