feat(pm/headscale): add hyperneutrino

Hyperneutrino is a friend of mine, and they have asked for access to the
headscale instance. Let's give them the standard permissions...

packetmix/systems/teal/headscale.nix

···
     */
     "group:users" = [
       "coded@"
+      "hyperneutrino@"
       "matei@"
       "minion@"
       "mostlyturquoise@"