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/i18n/en.ts

@@ -960,4 +960,61 @@ export const en: Translations = {
     topProductsEmptyTitle: 'No product sales in this period',
     topProductsEmptyDescription: 'Try a wider date range.',
   },
+  adminShell: {
+    skipToContent: 'Skip to content',
+    openSidebar: 'Open menu',
+    closeSidebar: 'Close menu',
+    collapseSidebar: 'Collapse menu',
+    expandSidebar: 'Expand menu',
+    nav: {
+      dashboard: 'Dashboard',
+      catalogGroup: 'Catalog',
+      products: 'Products',
+      categories: 'Categories',
+      orders: 'Orders',
+      transactions: 'Transactions',
+      reviews: 'Reviews',
+      reports: 'Reports',
+      content: 'Content',
+      mediaLibrary: 'Media Library',
+      marketplaceBuilder: 'Marketplace Builder',
+      users: 'Users',
+      settings: 'Settings',
+      monitoring: 'Monitoring',
+      analytics: 'Analytics',
+      documentation: 'Documentation',
+      help: 'Help',
+      logout: 'Log out',
+      comingSoonBadge: 'Soon',
+    },
+    topbar: {
+      searchLabel: 'Search the admin panel',
+      searchPlaceholder: 'Search products, orders, pages...',
+      notifications: 'Notifications',
+      notificationsEmpty: 'No new notifications',
+      account: 'Admin account',
+      tenantSelector: 'Store',
+      tenantSelectorComingSoon: 'Switching between stores is coming soon',
+      quickPublish: 'Publish',
+      quickPublishComingSoon: 'Quick publish is coming soon',
+    },
+    breadcrumbHome: 'Admin',
+    pages: {
+      dashboard: { title: 'Dashboard', description: 'An overview of your marketplace' },
+      products: { title: 'Products', description: 'Manage product listings and their visibility' },
+      productCreate: { title: 'New product', description: 'Fill in the details to add a product to the catalog' },
+      productEdit: { title: 'Edit product', description: 'Change this product\'s details' },
+      productDuplicate: { title: 'Duplicate product', description: 'Create a new product based on an existing one' },
+      categories: { title: 'Categories', description: 'Build your catalog\'s category tree' },
+      categoryCreate: { title: 'New category', description: 'Add a category to the catalog tree' },
+      categoryEdit: { title: 'Edit category', description: 'Change this category\'s details' },
+      orders: { title: 'Orders', description: 'View and process customer orders' },
+      orderDetail: { title: 'Order', description: 'Order details and status' },
+      transactions: { title: 'Transactions', description: 'Payments, refunds, and fraud review' },
+      media: { title: 'Media Library', description: 'Images and files for products and pages' },
+      users: { title: 'Users', description: 'Admin team members and permissions' },
+      monitoring: { title: 'Monitoring', description: 'Queue, webhook, and system event status' },
+      analytics: { title: 'Analytics', description: 'Sales, products, and shopper behavior' },
+    },
+  },
 };