Keep routers and the installer running with the lid closed

logind suspends laptops on lid close by default; a router (and an install
in progress) must keep running.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AeFqV9dZrK6nipHkPfyM4F

modules/installer/iso.nix

@@ -16,6 +16,13 @@
   isoImage.volumeID = "ROUTER_INSTALL";
   isoImage.squashfsCompression = "zstd -Xcompression-level 6";
 
+  # Installing on a laptop must survive closing its lid.
+  services.logind.settings.Login = {
+    HandleLidSwitch = "ignore";
+    HandleLidSwitchExternalPower = "ignore";
+    HandleLidSwitchDocked = "ignore";
+  };
+
   services.openssh = {
     enable = true;
     settings.PermitRootLogin = "prohibit-password";