feat(registry): validate unique addresses and routes

registry/route.nix

@@ -1,5 +1,12 @@
 { lib, ... }:
 {
+  checks = [
+    {
+      assertion = lib.registry.predicates.uniqueValue (entry: entry.value.domain);
+      message = "Route domains must be unique.";
+    }
+  ];
+
   type = lib.types.submodule {
     options = {
       domain = lib.mkOption {