services: add jellyfin, archivebox, custom dns

- `internal.thegeneralist01.com` and `archive.thegeneralist01.com` are
  not public. I have Split DNS enabled on them (in Tailscale), with the
  IP of the DNS server set to a private Tailscale IP of my home server;
- CoreDNS (also on my home server) is used to resolve the two private
  domains' IPs to the home server itself;
- nginx only listens to its machine's (home server's) Tailscale IP;
- Therefore, all of it is hermetic!

modules/linux/dns.nix

@@ -1,8 +1,7 @@
 { config, lib, ... }: let
-  inherit (lib) concatStringsSep;
+  inherit (lib) mkIf concatStringsSep;
 in {
-  # TODO: add fallback & check other options
-  services.resolved = {
+  services.resolved = mkIf (!config.isServer) {
     enable = true;
 
     extraConfig = config.dnsServers