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/services/index.ts

@@ -1,6 +1,5 @@
 export * from './api.service';
 export * from './cart.service';
-export * from './telegram.service';
 export * from './language.service';
 export * from './seo.service';
 export * from './location.service';

src/app/services/telegram.service.ts

@@ -1,39 +0,0 @@
-import { Injectable } from '@angular/core';
-import type { } from '../types/telegram.types';
-
-@Injectable({
-  providedIn: 'root'
-})
-export class TelegramService {
-  private tg = typeof window !== 'undefined' ? window.Telegram?.WebApp : null;
-
-  isTelegramApp(): boolean {
-    return !!this.tg;
-  }
-
-  getUser() {
-    return this.tg?.initDataUnsafe?.user || null;
-  }
-
-  getUserId(): number | null {
-    return this.tg?.initDataUnsafe?.user?.id || null;
-  }
-
-  getUsername(): string | null {
-    return this.tg?.initDataUnsafe?.user?.username || null;
-  }
-
-  getFirstName(): string | null {
-    return this.tg?.initDataUnsafe?.user?.first_name || null;
-  }
-
-  getFullName(): string | null {
-    const user = this.getUser();
-    if (!user) return null;
-    return `${user.first_name}${user.last_name ? ' ' + user.last_name : ''}`;
-  }
-
-  getDisplayName(): string {
-    return this.getUsername() || this.getFullName() || 'User';
-  }
-}