fix(pxe-boot): disable dnsmasq DNS listener to avoid port 53 conflict

dnsmasq binds port 53 by default even when only proxy DHCP is needed.
systemd-resolved already owns port 53 on the pxe-boot container, so
dnsmasq crashes at startup. Setting port=0 disables the DNS listener
entirely — pxe-boot only needs the proxy DHCP path for iPXE chainloading.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

modules/build-types/pxe-boot.nix

@@ -423,6 +423,10 @@ in
   services.dnsmasq = {
     enable = true;
     settings = {
+      # Disable DNS listener — only proxy DHCP is needed here.
+      # Without this dnsmasq tries to bind port 53 which systemd-resolved
+      # already owns, causing startup failure.
+      port = 0;
       dhcp-range = [ "192.168.2.0,proxy" ];
       dhcp-match = [
         "set:ipxe,175"