feat(admin): implement analytics and monitoring center

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

- Business Dashboard: revenue/orders/customers/AOV/top products/low stock/recent activity/warnings/completion% (Overview tab)
- Marketplace Health: real completion checks (images, SEO, categories, reviews, orders, translations, homepage, backend, performance) with clickable recommendations
- Product Analytics: top selling/most reviewed/worst rated/hidden/archived counts; top-viewed honestly marked Unknown (no view tracking exists)
- Customer Analytics: new/returning customers, average spend, retention - derived from real order data
- Search & Traffic tabs: honest 'Unknown - available after backend integration' placeholders, no fabricated numbers
- Recommendations engine: actionable cards (missing images/SEO/category, empty categories, incomplete homepage, unpublished static pages) linking to the relevant admin page
- System Monitoring: added real draft/publish/sync/backend-connectivity state from AdminDashboardFacade
- CSV export extended to top products and health checks; added print action
- New adminAnalytics.* and adminMarketplaceHealth.* i18n namespaces (en/ru/hy), no raw i18n keys
- Reused existing shared UI (app-table/app-badge/app-skeleton/app-empty-state) and content-health-widget completion-meter pattern - no new backend APIs, no storage changes

src/app/features/admin/analytics/models/admin-analytics.model.ts

@@ -7,6 +7,9 @@ export interface AdminAnalyticsSummary {
   avgOrderValue: number;
   productsCount: number;
   categoriesCount: number;
+  customersCount: number;
+  /** null = unknown - no visitor/traffic tracking exists yet. Never fabricated. */
+  conversionRate: number | null;
 }
 
 export interface AdminAnalyticsSeriesPoint {
@@ -20,3 +23,59 @@ export interface AdminAnalyticsTopProduct {
   quantity: number;
   revenue: number;
 }
+
+export interface AdminLowStockProduct {
+  productId: string;
+  name: string;
+  quantity: number;
+  stockStatus: 'low_stock' | 'out_of_stock';
+}
+
+export interface AdminRecentActivityEntry {
+  id: string;
+  labelKey: string;
+  timestamp: number;
+}
+
+export type AdminMarketplaceHealthStatus = 'healthy' | 'attention' | 'unhealthy' | 'unknown';
+
+export interface AdminMarketplaceHealthCheck {
+  code: string;
+  labelKey: string;
+  status: AdminMarketplaceHealthStatus;
+  displayValue?: string | null;
+  actionRoute?: string[];
+}
+
+export interface AdminProductAnalyticsRow {
+  productId: string;
+  name: string;
+  value: number;
+}
+
+export interface AdminProductAnalytics {
+  topSelling: AdminAnalyticsTopProduct[];
+  mostReviewed: AdminProductAnalyticsRow[];
+  worstRated: AdminProductAnalyticsRow[];
+  hiddenCount: number;
+  archivedCount: number;
+}
+
+export interface AdminCustomerAnalytics {
+  newCustomers: number;
+  returningCustomers: number;
+  averageSpend: number;
+  currency: string;
+  /** null = unknown when there are no customers in range to compute a rate from. */
+  retentionPercent: number | null;
+}
+
+export type AdminRecommendationSeverity = 'info' | 'warning' | 'critical';
+
+export interface AdminRecommendationCard {
+  id: string;
+  labelKey: string;
+  descriptionKey?: string;
+  severity: AdminRecommendationSeverity;
+  route: string[];
+}