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

ui/lib/runtime-config.ts

@@ -51,6 +51,8 @@ export async function getRuntimePublicConfig(): Promise<RuntimePublicConfig> {
     posthogUiHost: readGatedEnv("UI_POSTHOG_ENABLED", "UI_POSTHOG_UI_HOST"),
     reoDevClientId: readEnv("REO_DEV_CLIENT_ID"),
     cloudEnabled: readBoolEnv("UI_CLOUD_ENABLED"),
+    // Deployment gate only: per-user Registry access is still checked server-side.
+    registryEnabled: readBoolEnv("UI_REGISTRY_ENABLED"),
     // Off only when explicitly "false": invited users can still register.
     selfRegistrationEnabled: readOptOutEnv("UI_SELF_REGISTRATION_ENABLED"),
     // Install-level selector "legacy" | "metronome" | "false"; the client only