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/i18n/en.ts

@@ -512,6 +512,8 @@ export const en: Translations = {
     validationMissingWidget: 'A homepage section has a widget with no type.',
     validationDuplicateNavLinks: 'Two or more header navigation links are duplicates.',
     validationInvalidColors: 'One or more theme colors are not valid hex colors.',
+    validationMissingTranslations: 'Some content is missing translations for a supported language.',
+    validationInvalidLayouts: 'One or more layouts reference an unknown layout type.',
     statusDraft: 'Draft',
     statusPublished: 'Published',
     unsavedChanges: 'Unsaved changes',
@@ -530,6 +532,52 @@ export const en: Translations = {
     confirmResetDraft: 'This discards all unpublished changes and restores the last published configuration. Continue?',
     confirmResetSection: 'This discards unpublished changes in this section only. Continue?',
   },
+  dashboard: {
+    title: 'Dashboard',
+    subtitle: 'Overview of your marketplace',
+    cardMarketplaceStatus: 'Marketplace Status',
+    cardProjectName: 'Project Name',
+    cardCurrentTheme: 'Current Theme',
+    cardLanguages: 'Languages',
+    cardCategoriesCount: 'Categories',
+    cardProductsCount: 'Products',
+    cardOrders: 'Orders',
+    cardRevenue: 'Revenue',
+    cardLastPublish: 'Last Publish',
+    cardLastDraftSave: 'Last Draft Save',
+    cardBootstrapVersion: 'Bootstrap Version',
+    cardActiveLayout: 'Active Layout',
+    cardEnabledWidgets: 'Enabled Widgets',
+    stateLoading: 'Loading...',
+    stateEmpty: 'No data yet',
+    stateError: 'Could not load this card',
+    statePendingBackend: 'Awaiting backend integration',
+    never: 'Never',
+    quickActionsTitle: 'Quick Actions',
+    actionEditProject: 'Edit Project',
+    actionCategories: 'Categories',
+    actionProducts: 'Products',
+    actionStaticPages: 'Static Pages',
+    actionTransactions: 'Transactions',
+    actionOrders: 'Orders',
+    actionMediaLibrary: 'Media Library',
+    actionPreviewMarketplace: 'Preview Marketplace',
+    activityTitle: 'Recent Activity',
+    activityEmpty: 'No activity yet. Save or publish a change to see it here.',
+    activityDraftSaved: 'Draft saved',
+    activityPublished: 'Published',
+    healthTitle: 'System Health',
+    healthAllClear: 'All checks passed',
+    healthBootstrapValid: 'Bootstrap valid',
+    healthConfigurationValid: 'Configuration valid',
+    healthMissingTranslations: 'Missing translations',
+    healthInvalidColors: 'Invalid colors',
+    healthInvalidWidgetReferences: 'Invalid widget references',
+    healthInvalidLayouts: 'Invalid layouts',
+    comingSoonTitle: 'Coming soon',
+    comingSoonDescription: 'This section is not built yet. Check back in a future update.',
+    backToDashboard: 'Back to dashboard',
+  },
   staticPages: {
     notFound: 'Page not found',
     backHome: 'Back to home',