site-config: dedupe cross-host values, fix stale dark-reader urls, drop desktop 1g hugepages

new site-config.nix holds values previously duplicated across hosts:
  domain, old_domain, contact_email, timezone, binary_cache (url + pubkey),
  dns_servers, lan (cidr + gateway), hosts.{muffin,yarn} (ip/alias/ssh_host_key),
  ssh_keys.{laptop,desktop,ci_deploy}.

threaded through specialArgs on all three hosts + home-manager extraSpecialArgs +
homeConfigurations.primary + serverLib. service-configs.nix now takes
{ site_config } as a function arg and drops its https namespace; per-service
domains (gitea/matrix/ntfy/mollysocket/livekit/firefox-sync/grafana) are
derived from site_config.domain. ~15 service files and 6 vm tests migrated.

breakage fixes rolled in:
 - home/progs/zen/dark-reader.nix: 5 stale *.gardling.com entries in
   disabledFor rewritten to *.sigkill.computer (caddy 301s the old names so
   these never fired and the new sigkill urls were getting dark-reader applied)
 - modules/desktop-common.nix: drop unused hugepagesz=1G/hugepages=3
   kernelParams (no consumer on mreow or yarn; xmrig on muffin still reserves
   its own via services/monero/xmrig.nix)

verification: muffin toplevel is bit-identical to pre-refactor baseline.
mreow/yarn toplevels differ only in boot.json kernelParams + darkreader
storage.js (nix-diff verified). deployGuardTest and fail2banVaultwardenTest
(latter exercises site_config.domain via bitwarden.nix) pass.

services/bitwarden.nix

@@ -2,6 +2,7 @@
   config,
   lib,
   pkgs,
+  site_config,
   service_configs,
   ...
 }:
@@ -25,7 +26,7 @@
     configurePostgres = true;
     config = {
       # Refer to https://github.com/dani-garcia/vaultwarden/blob/main/.env.template
-      DOMAIN = "https://bitwarden.${service_configs.https.domain}";
+      DOMAIN = "https://bitwarden.${site_config.domain}";
       SIGNUPS_ALLOWED = false;
 
       ROCKET_ADDRESS = "127.0.0.1";
@@ -34,7 +35,7 @@
     };
   };
 
-  services.caddy.virtualHosts."bitwarden.${service_configs.https.domain}".extraConfig = ''
+  services.caddy.virtualHosts."bitwarden.${site_config.domain}".extraConfig = ''
     encode zstd gzip
 
     reverse_proxy :${toString config.services.vaultwarden.config.ROCKET_PORT} {