feat(bootstrap): fall back to built-in placeholder when marketplace unpublished

Adds published: boolean to the bootstrap wire contract. ConfigService
swaps to a new DEFAULT_BOOTSTRAP constant (all feature flags on, generic
branding/theme/pages) whenever the backend reports published: false, so
an unpublished marketplace renders a working demo instead of a blank or
broken page. Missing published field stays backward compatible (treated
as true). Documents the brand bootstrap wire shape for backend/ops use.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/shared/models/config/bootstrap-config.model.ts

@@ -24,6 +24,7 @@ import { WidgetRegistryConfig } from './widget-registry.model';
 export interface BootstrapConfig {
   schemaVersion: string;
   generatedAt: string;
+  published: boolean;
   tenant: TenantConfig;
   branding: BrandingConfig;
   theme: ThemeConfig;