fix: review findings from full-diff audit (7 fixed)

- popularSearches sent translated display text as the actual search
  query instead of the canonical term - useSuggestion() now prefers
  target.query.q when present.
- CartService.addItem() dedup guard resolved immediately instead of
  awaiting the real in-flight add; now tracks the pending Promise per
  itemID so concurrent callers await the actual result.
- addItem()'s Promise never rejected on failure (resolve() in both
  next/error branches) - now rejects on error; buyNow() catches and
  shows an error toast instead of navigating on a failed add.
- Quick View had no stale-response guard - a slower earlier request
  could overwrite a faster later one. Added a request-generation
  counter.
- cart autoSubmitPurchase() set paymentStatus to null synchronously
  right after firing the async submit call, blanking the success
  screen while the request was still in flight. Removed the
  redundant/harmful line.
- Order terminal-status guard (cancelled/refunded can't be reopened)
  lived only in the page component. Moved enforcement into the
  gateway (single write path) via a shared TERMINAL_ORDER_STATUSES
  const, so no future caller can bypass it.
- TranslatePipe's per-instance memoization cache had no eviction,
  so bindings with volatile params (pagination counts) grew it
  unbounded for the component's lifetime. Capped at 50 entries.

Not changed: the dark-mode color override was flagged as clobbering
admin branding, but it's the exact palette explicitly requested this
session for the global dark default - not a bug.

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

src/app/i18n/translate.pipe.ts

@@ -11,6 +11,9 @@ import { LanguageService } from '../services/language.service';
  * nothing actually changed - hit a Map lookup instead of re-walking the
  * translation tree and re-running the interpolation regex.
  */
+/** Bindings with volatile params (pagination counts, etc.) would otherwise grow this cache for the component's whole lifetime. */
+const MAX_CACHE_ENTRIES = 50;
+
 @Pipe({
   name: 'translate',
   pure: false,
@@ -36,6 +39,9 @@ export class TranslatePipe implements PipeTransform {
     }
 
     const result = this.translateService.t(key, params);
+    if (this.cache.size >= MAX_CACHE_ENTRIES) {
+      this.cache.clear();
+    }
     this.cache.set(cacheKey, result);
     return result;
   }