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/router/power.nix

@@ -0,0 +1,12 @@
+# A router keeps routing with the lid shut: laptops make fine routers, but
+# logind suspends them on lid close by default.
+{ config, lib, ... }:
+{
+  config = lib.mkIf config.router.enable {
+    services.logind.settings.Login = {
+      HandleLidSwitch = "ignore";
+      HandleLidSwitchExternalPower = "ignore";
+      HandleLidSwitchDocked = "ignore";
+    };
+  };
+}