fix(backoffice): add error+retry states to Users, Monitoring, Analytics, Reports

Phase 8 (RC-01): these 4 list/dashboard pages had no error-state handling
on their primary data-load subscriptions — on a gateway error, `loading`
was either never reset (Users, Monitoring, Analytics: genuine infinite-
spinner risk, nested subscribe chain in Analytics never resolved on
failure) or there was no loading/empty/error handling at all (Reports
queue: raw table with zero skeleton or fallback).

- admin-users.facade.ts, admin-monitoring.facade.ts: add `error` signal,
  error callback on the primary load subscribe so `loading` always
  resolves.
- admin-analytics.facade.ts: add `error` signal; every level of the
  4-deep nested gateway subscribe chain (orders -> products ->
  categories -> reviews) now has an error handler that resolves loading
  instead of leaving it stuck true.
- admin-moderation.facade.ts: add `reportsLoading`/`reportsError` signals
  (reports list had none previously).
- Templates: reuse existing `app-skeleton`/`app-empty-state`/`app-button`
  primitives for the new error branch, `common.retry` label, two new
  generic `common.errorTitle`/`common.errorDescription` i18n keys added
  to en/ru/hy (reused across all 4 fixes instead of one-off per-page
  copy).

Verified: tsc --noEmit clean, `npm run build` green (pre-existing bundle-
budget warning only, unrelated). Live-checked Home (375px) and Backoffice
Products (1024px) — no console errors, tables/cards render without
overflow.

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

src/app/features/admin/users/facade/admin-users.facade.ts

@@ -11,6 +11,7 @@ export class AdminUsersFacade {
   readonly roles = signal<AdminRole[]>([]);
   readonly invitations = signal<AdminInvitation[]>([]);
   readonly loading = signal(false);
+  readonly error = signal(false);
   readonly sessionsTarget = signal<AdminUser | null>(null);
   readonly sessions = signal<AdminSession[]>([]);
   readonly auditTarget = signal<AdminUser | null>(null);
@@ -18,7 +19,11 @@ export class AdminUsersFacade {
 
   loadAll(): void {
     this.loading.set(true);
-    this.gateway.loadUsers().pipe(take(1)).subscribe(users => { this.users.set(users); this.loading.set(false); });
+    this.error.set(false);
+    this.gateway.loadUsers().pipe(take(1)).subscribe({
+      next: users => { this.users.set(users); this.loading.set(false); },
+      error: () => { this.users.set([]); this.loading.set(false); this.error.set(true); }
+    });
     this.gateway.loadRoles().pipe(take(1)).subscribe(roles => this.roles.set(roles));
     this.gateway.loadInvitations().pipe(take(1)).subscribe(invitations => this.invitations.set(invitations));
   }