chore(cleanup): Phase 1 - remove dead code, fix orphaned SeoService wiring

Ran knip to find unused exports/dependencies (deps already clean, no
unused packages/files found).

Removed genuinely dead code (verified zero references anywhere,
including templates):
- 4 unused constants in config/constants.ts (scroll/pagination/search
  thresholds never consumed)
- isAdminRole(), toSearchResult(), createInitialSearchState(),
  getTranslatedCategoryName() - unused utility functions
- DEFAULT_EDITOR_HEADER_CONFIG - unused constant
- TelegramService - entire file deleted; cart.component.ts/
  cart.service.ts already implement the same window.Telegram.WebApp
  access directly, this was an unused duplicate

Real bug fix found during the sweep: SeoService has providedIn:'root'
with a live effect() meant to sync <title>/OG/canonical tags to
tenant bootstrap config, but nothing in the app ever injected it, so
Angular never instantiated it and the effect never ran - the SEO sync
a prior sprint reported as "done and verified" was actually dead on
arrival. Fixed by injecting SeoService in the root App component.

Left alone: ~125 knip-flagged "unused exported types" - overwhelmingly
config/schema interfaces for the widget/theme/admin domain models,
high false-positive rate for this kind of interface-heavy Angular app,
deleting blind risks breaking structural type contracts. Also left
locally-used-but-over-exported helpers (toCssColor/toBackendColor,
HTML_EDITOR_TOOLBAR*, HISTORY_LIMIT, DEFAULT_CATALOG_PAGE_SIZE) - real
code, not dead, just exported wider than needed.

tsc --noEmit and ng build --configuration=production both clean (only
pre-existing bundle-budget warning, unrelated).

Files changed: src/app/app.ts, src/app/config/constants.ts,
src/app/core/auth/models/permission.model.ts,
src/app/core/products/models/catalog-experience.model.ts,
src/app/core/search/models/search-state.model.ts,
src/app/features/project-editor/models/project-editor.model.ts,
src/app/services/index.ts, src/app/utils/item.utils.ts,
src/app/services/telegram.service.ts (deleted)

src/app/app.ts

@@ -14,6 +14,7 @@ import { TranslateService } from './i18n/translate.service';
 import { PlatformRuntimeService } from './core/runtime/platform-runtime.service';
 import { UiRuntimeFacade } from './facades/runtime/ui-runtime.facade';
 import { ApiHealthService } from './services/api-health.service';
+import { SeoService } from './services/seo.service';
 import { FloatingNotificationsComponent } from './features/website/user-experience/components/floating-notifications/floating-notifications.component';
 import { AdminAuthService } from './core/admin-auth/admin-auth.service';
 import { AuthService } from './services/auth.service';
@@ -42,6 +43,7 @@ export class App implements OnInit {
   private platformRuntime = inject(PlatformRuntimeService);
   private uiRuntime = inject(UiRuntimeFacade);
   private apiHealth = inject(ApiHealthService);
+  private seoService = inject(SeoService);
   private authService = inject(AuthService);
   private adminAuthService = inject(AdminAuthService);