revert bd3861c580

revert Merge pull request 'Remove clanModules/*' (#4202) from remove-modules into main

Reviewed-on: https://git.clan.lol/clan/clan-core/pulls/4202

See: https://git.clan.lol/clan/clan-core/issues/4365

Not all modules are migrated.
If they are not migrated, we need to write migration docs and please display the link to the migration docs

clanModules/zt-tcp-relay/README.md

@@ -0,0 +1,3 @@
+---
+description = "Enable ZeroTier VPN over TCP for networks where UDP is blocked."
+---

clanModules/zt-tcp-relay/default.nix

@@ -0,0 +1,35 @@
+{
+  pkgs,
+  lib,
+  config,
+  ...
+}:
+{
+  options.clan.zt-tcp-relay = {
+    port = lib.mkOption {
+      type = lib.types.port;
+      default = 4443;
+      description = "Port to listen on";
+    };
+  };
+  config = {
+    warnings = [
+      "The clan.zt-tcp-relay module is deprecated and will be removed on 2025-07-15. Please migrate to user-maintained configuration."
+    ];
+
+    networking.firewall.allowedTCPPorts = [ config.clan.zt-tcp-relay.port ];
+
+    systemd.services.zt-tcp-relay = {
+      wantedBy = [ "multi-user.target" ];
+      after = [ "network.target" ];
+      serviceConfig = {
+        ExecStart = "${
+          pkgs.callPackage ../../pkgs/zt-tcp-relay { }
+        }/bin/zt-tcp-relay --listen [::]:${builtins.toString config.clan.zt-tcp-relay.port}";
+        Restart = "always";
+        RestartSec = "5";
+        dynamicUsers = true;
+      };
+    };
+  };
+}