feat(remote-build): Add john-endesktop as builder machine

- Enable enableBuilder role on john-endesktop
- Add john-endesktop to nix-book's builder list (maxJobs=1, speedFactor=1)
- Document SSH setup process for new clients in remote-build role

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

roles/remote-build/default.nix

@@ -1,3 +1,66 @@
+# Remote Build Role
+#
+# This module configures Nix distributed builds, allowing machines to offload
+# builds to more powerful remote machines.
+#
+# SETUP INSTRUCTIONS
+# ==================
+#
+# 1. BUILDER MACHINE SETUP
+#    On machines that will serve as builders (e.g., zix790prors, john-endesktop):
+#
+#    a) Enable the builder role in configuration.nix:
+#       roles.remote-build.enableBuilder = true;
+#
+#    b) After nixos-rebuild, the nix-builder user is created automatically.
+#       You need to add client SSH public keys to the builder. Either:
+#
+#       Option A - Manual (recommended for initial setup):
+#         sudo mkdir -p /var/lib/nix-builder/.ssh
+#         sudo bash -c 'cat >> /var/lib/nix-builder/.ssh/authorized_keys' << 'EOF'
+#         ssh-ed25519 AAAA... root@client-hostname
+#         EOF
+#         sudo chown -R nix-builder:nix-builder /var/lib/nix-builder/.ssh
+#         sudo chmod 700 /var/lib/nix-builder/.ssh
+#         sudo chmod 600 /var/lib/nix-builder/.ssh/authorized_keys
+#
+#       Option B - Via NixOS config (if you store keys in the repo):
+#         users.users.nix-builder.openssh.authorizedKeys.keys = [
+#           "ssh-ed25519 AAAA... root@client-hostname"
+#         ];
+#
+# 2. CLIENT MACHINE SETUP
+#    On machines that will use remote builders (e.g., nix-book):
+#
+#    a) Configure builders in configuration.nix:
+#       roles.remote-build.builders = [
+#         {
+#           hostName = "zix790prors";
+#           maxJobs = 16;      # Number of parallel build jobs
+#           speedFactor = 3;   # Higher = prefer this builder
+#         }
+#         {
+#           hostName = "john-endesktop";
+#           maxJobs = 1;       # Conservative for busy machines
+#           speedFactor = 1;
+#         }
+#       ];
+#
+#    b) Generate SSH key for root (if not exists) and copy to builders:
+#       sudo ssh-keygen -t ed25519 -f /root/.ssh/id_ed25519 -N ""
+#       sudo cat /root/.ssh/id_ed25519.pub  # Add this to builder's authorized_keys
+#
+#    c) Accept the builder's host key (as root):
+#       sudo ssh nix-builder@zix790prors echo "Connected!"
+#       sudo ssh nix-builder@john-endesktop echo "Connected!"
+#
+# 3. VERIFY SETUP
+#    Test that distributed builds work:
+#      nix build --rebuild nixpkgs#hello --print-build-logs
+#
+#    Check builder connectivity:
+#      nix store ping --store ssh-ng://nix-builder@zix790prors
+#
 { lib, config, pkgs, ... }:
 
 with lib;