feat(nixos): migrate system configuration

configs/nixos/registry/address.nix

@@ -0,0 +1,11 @@
+{ lib, ... }:
+{
+  type = lib.types.str;
+
+  checks = [
+    {
+      assertion = lib.registry.predicates.uniqueValue (entry: entry.value);
+      message = "Address registry values must be unique.";
+    }
+  ];
+}