Authorize the WSL workstation as a nix-cache remote-builder client

Adds debian@surface's existing SSH key (already used as its admin
key elsewhere in this repo) to vars.remoteBuilderAuthorizedKeys so
nix-cache will accept it as a distributed-build client once deployed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01La55Nsss8jZ7ZuzUV9mfot

modules/pxe-boot/stage-installer-artifacts.nix

@@ -0,0 +1,23 @@
+{ netbootSystem, ... }:
+
+let
+  # config.system.build.kernel and .netbootRamdisk are directories, not the
+  # files themselves — nixpkgs' own system.build.kexecTree does the same
+  # ${...}/<file> dereference for the same reason.
+  inherit (netbootSystem.config.system.boot.loader) kernelFile;
+in
+{
+  # Builds this flake's own installer netboot image (the same one
+  # `nix build .#pxe` produces) and stages it where menu.ipxe's :nixos
+  # entry expects it, so the pxe-boot host is self-contained — no manual
+  # operator step to populate /srv/pxe/http/nixos after deploy.
+  systemd.tmpfiles.rules = [
+    # Declared here too (not just in build-types/pxe-boot.nix) so this
+    # module's C+ rules don't depend on cross-module list-merge ordering —
+    # tmpfiles' C type needs the target directory to already exist.
+    "d /srv/pxe/http/nixos 0755 root root -"
+    "C+ /srv/pxe/http/nixos/${kernelFile} 0644 root root - ${netbootSystem.config.system.build.kernel}/${kernelFile}"
+    "C+ /srv/pxe/http/nixos/initrd 0644 root root - ${netbootSystem.config.system.build.netbootRamdisk}/initrd"
+    "C+ /srv/pxe/http/nixos/netboot.ipxe 0644 root root - ${netbootSystem.config.system.build.netbootIpxeScript}/netboot.ipxe"
+  ];
+}