fix compile error

Author: isXander

src/main/java/dev/isxander/controlify/Controlify.java

@@ -197,7 +197,7 @@ public GuideDomainRegistry<ContainerCtx> container() {
                             }
 
                             @Override
-                            public <T extends FactCtx> GuideDomainRegistry<T> registerCustom(GuideDomain<T> domain) {
+                            public <T extends FactCtx> RenderableGuideDomain<T> registerCustom(GuideDomain<T> domain) {
                                 GuideDomains.CUSTOM_DOMAINS.put(domain.id(), domain);
                                 PlatformClientUtil.registerAssetReloadListener(domain);
                                 return domain;