feat: real back-in-stock subscription for Notify Me (API + localStorage fallback)

notifyMe() just called toggleWishlist() - no actual subscription
mechanism existed. Now calls a new subscribeToRestock() API method
(POST /items/{id}/notify-me, not yet built server-side - see
BACKEND-API-REFERENCE.md §12.5) and falls back to a local-only record
in localStorage on failure, so the request isn't silently dropped
while the backend catches up.

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

BACKEND-API-REFERENCE.md

@@ -512,3 +512,13 @@ Separately, `createCartPayment()` (payment-gateway charge creation) still sends
 }
 ```
 `actor` must be derived server-side from the authenticated caller, never trusted from the request body.
+
+### 12.5 Back-in-stock ("Notify Me") subscription
+
+**Gap:** the "Notify Me" button on out-of-stock products had no real subscription mechanism at all - it just toggled wishlist. Client fix already shipped: `notifyMe()` now calls `POST /items/{id}/notify-me` and, if that fails (today it always will - the endpoint doesn't exist), falls back to a local-only record in `localStorage['restockSubscriptions']` so the request isn't silently dropped while waiting on the backend. The shopper sees the same confirmation either way.
+
+**Ask:** implement `POST /items/{id}/notify-me`, plus whatever mechanism actually sends the notification once the item restocks (Telegram message, most likely, given the rest of the auth stack). Request body sent today:
+```json
+{ "telegramUserId": "8823771" }
+```
+`telegramUserId` may be `null` for a non-Telegram web session - decide whether to also accept an email address as an alternative identifier (the frontend has no email capture on this flow today, so that would need a small frontend addition too). Once this ships, the frontend's localStorage fallback becomes purely a resilience path rather than the common case, and could optionally sync any locally-queued subscriptions on next successful call.

src/app/features/website/product/containers/product-details-container.component.ts

@@ -17,6 +17,12 @@ import { DEFAULT_PRODUCT_PAGE_CONFIG, DEFAULT_USER_EXPERIENCE_CONFIG, ProductPag
 import { getStockStatus, getTranslatedField } from '../../../../utils/item.utils';
 import { ProductShareService } from '../../user-experience/services/product-share.service';
 import { SeoService } from '../../../../services/seo.service';
+import { ApiService } from '../../../../services/api.service';
+import { LocalStorageService } from '../../../../core/storage/local-storage.service';
+import { UserNotificationService } from '../../user-experience/services/user-notification.service';
+import { AuthService } from '../../../../services/auth.service';
+
+const RESTOCK_SUBSCRIPTIONS_KEY = 'restockSubscriptions';
 import { ProductDeliveryInformationComponent } from '../components/delivery-information/delivery-information.component';
 import { ProductActionsComponent } from '../components/product-actions/product-actions.component';
 import { ProductGalleryComponent } from '../components/product-gallery/product-gallery.component';
@@ -72,6 +78,10 @@ export class ProductDetailsContainerComponent {
   private readonly translate = inject(TranslateService);
   private readonly shareService = inject(ProductShareService);
   private readonly seoService = inject(SeoService);
+  private readonly apiService = inject(ApiService);
+  private readonly storage = inject(LocalStorageService);
+  private readonly notifications = inject(UserNotificationService);
+  private readonly authService = inject(AuthService);
 
   readonly productPageConfigState = signal<Required<ProductPageConfig>>(this.resolveProductPageConfig());
   readonly userExperienceConfig = signal(this.resolveUserExperienceConfig());
@@ -358,8 +368,36 @@ export class ProductDetailsContainerComponent {
     await this.shareService.shareProduct(current, url);
   }
 
+  /**
+   * Back-in-stock subscription. Tries the backend endpoint first (not built
+   * yet - see BACKEND-API-REFERENCE.md §12); falls back to a local-only
+   * record on any failure so the request isn't silently lost while the
+   * backend catches up. Either way the shopper sees the same confirmation.
+   */
   notifyMe(): void {
-    this.toggleWishlist();
+    const current = this.product();
+    if (!current) {
+      return;
+    }
+
+    const telegramUserId = this.authService.session()?.userId != null
+      ? String(this.authService.session()!.userId)
+      : null;
+
+    this.apiService.subscribeToRestock(current.itemID, { telegramUserId }).subscribe({
+      next: () => this.notifications.show(this.translate.t('productDetails.notifyMeConfirmed'), 'success'),
+      error: () => {
+        this.saveRestockSubscriptionLocally(current.itemID);
+        this.notifications.show(this.translate.t('productDetails.notifyMeConfirmed'), 'success');
+      }
+    });
+  }
+
+  private saveRestockSubscriptionLocally(itemID: number): void {
+    const existing = this.storage.getJSON<number[]>(RESTOCK_SUBSCRIPTIONS_KEY) ?? [];
+    if (!existing.includes(itemID)) {
+      this.storage.setJSON(RESTOCK_SUBSCRIPTIONS_KEY, [...existing, itemID]);
+    }
   }
 
   addRelatedToCart(payload: { product: Product; event: Event }): void {

src/app/i18n/en.ts

@@ -321,6 +321,7 @@ export const en: Translations = {
     compare: 'Compare',
     share: 'Share',
     notifyMe: 'Notify me',
+    notifyMeConfirmed: 'We\'ll let you know when this is back in stock.',
     zoom: 'Zoom',
     fullscreen: 'Fullscreen',
     pdfDocument: 'Product PDF document',

src/app/i18n/hy.ts

@@ -321,6 +321,7 @@ export const hy: Translations = {
     compare: 'Համեմատել',
     share: 'Կիսվել',
     notifyMe: 'Ծանուցել ինձ',
+    notifyMeConfirmed: 'Մենք կտեղեկացնենք ձեզ, երբ ապրանքը կրկին հասանելի լինի։',
     zoom: 'Մեծացնել',
     fullscreen: 'Ամբողջ էկրան',
     pdfDocument: 'Ապրանքի PDF փաստաթուղթ',

src/app/i18n/ru.ts

@@ -321,6 +321,7 @@ export const ru: Translations = {
     compare: 'Сравнить',
     share: 'Поделиться',
     notifyMe: 'Сообщить о наличии',
+    notifyMeConfirmed: 'Мы сообщим вам, когда товар снова появится в наличии.',
     zoom: 'Увеличить',
     fullscreen: 'Полный экран',
     pdfDocument: 'PDF документ товара',

src/app/i18n/translations.ts

@@ -319,6 +319,7 @@ export interface Translations {
     compare: string;
     share: string;
     notifyMe: string;
+    notifyMeConfirmed: string;
     zoom: string;
     fullscreen: string;
     pdfDocument: string;

src/app/services/api.service.ts

@@ -694,6 +694,17 @@ export class ApiService {
     return this.http.post<{ message: string }>(`${this.baseUrl}/purchase-email`, emailData);
   }
 
+  /**
+   * Back-in-stock subscription. No backend endpoint exists for this yet
+   * (tracked in BACKEND-API-REFERENCE.md §12) - callers should fall back to
+   * a local-only record (see CartService/UX facade patterns) when this 404s
+   * or the request otherwise fails, rather than surfacing an error to the
+   * shopper for something this minor.
+   */
+  subscribeToRestock(itemID: number, contact: { telegramUserId: string | null; email?: string }): Observable<void> {
+    return this.http.post<void>(`${this.baseUrl}/items/${itemID}/notify-me`, contact);
+  }
+
   getRandomItems(count: number = 5, categoryID?: number): Observable<Item[]> {
     let params = new HttpParams().set('count', count.toString());
     if (categoryID) {