fix(ui): stop the add-provider modal from shifting while it loads (#13179)

ui/lib/shared/env.ts

@@ -21,6 +21,21 @@ export function isCloud(): boolean {
   return readBoolEnv("UI_CLOUD_ENABLED");
 }
 
+/**
+ * Whether this Cloud deployment offers Registry providers (`UI_REGISTRY_ENABLED`).
+ *
+ * Read from the island in the browser, then the env, like `isCloud()`. It only
+ * gates the deployment: per-user Registry access is still decided server-side.
+ */
+export function isRegistryEnabled(): boolean {
+  if (!isCloud()) return false;
+
+  const islandConfig = readRuntimeConfigIsland();
+  if (islandConfig) return islandConfig.registryEnabled;
+
+  return readBoolEnv("UI_REGISTRY_ENABLED");
+}
+
 /**
  * Whether visitors can create an account without an invitation.
  *