feat(admin): build shared admin shell

Sidebar (Dashboard/Catalog group/Products/Categories/Orders/Transactions/
Reviews/Reports/Content/Media/Marketplace Builder/Users/Settings/
Monitoring/Analytics + Documentation/Help/Logout), sticky topbar
(breadcrumbs, page title/description, search, notifications, tenant
selector and quick-publish placeholders, current user), reserved
right-rail slot, scrollable content area. Desktop 280px sidebar, tablet
icon rail, mobile drawer with focus management and Escape-to-close.

Nav items without a built page (Reviews, Reports, Settings, Docs, Help)
render disabled with a coming-soon badge instead of dead links; Content
and Marketplace Builder route to the existing project-editor pages
(static-pages / general) rather than duplicating them.

All 15 /backoffice/** routes now render through AdminLayoutComponent;
the public storefront header/back-button/footer no longer render on
admin routes (app.ts/app.html gate on a new isAdminRoute signal).

Added the adminShell i18n namespace (ru/en/hy) for every new shell
string so this doesn't add to the existing untranslated-admin-UI gap
tracked in KNOWN-ISSUES.md.

Colors/type sizes follow DESIGN.md tokens; the two rgba() modal-scrim
values are a documented, intentional exception (neutral overlay,
not a themed token).

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

src/app/app.html

@@ -10,6 +10,9 @@
     <p>{{ 'app.serverError' | translate }}</p>
     <button class="retry-btn" (click)="retryConnection()">{{ 'app.retryConnection' | translate }}</button>
   </div>
+} @else if (isAdminRoute()) {
+  <router-outlet></router-outlet>
+  <app-telegram-login mode="admin" />
 } @else {
   <app-header></app-header>
   <main class="main-content">