feat(admin): sprint 19 admin dashboard, routing, i18n

- Add admin dashboard feature (models/gateway/facade/components/page)
- Wire admin/products routes and backoffice coming-soon placeholders
- Add lastPublishedAt to ProjectEditorFacade/state
- Add dashboard i18n keys (en/ru/hy) and docs/ADMIN.md

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

src/app/features/project-editor/models/project-editor.model.ts

@@ -22,6 +22,7 @@ export interface ProjectEditorState {
   status: 'draft' | 'published';
   lastSavedBootstrap: BootstrapConfig | null;
   lastSavedAt: number | null;
+  lastPublishedAt: number | null;
   draftRestored: boolean;
 }