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/default.nix

@@ -9,5 +9,6 @@
     ./dhcp.nix
     ./dns.nix
     ./rollback.nix
+    ./power.nix
   ];
 }