fix: improve locale detection in 404 page to match middleware logic

- Add detectLocale function that checks URL path first, then cookie, then accept-language header
- Use getLocaleFromPath helper to extract locale from URL
- Import LOCALE_COOKIE constant for consistency
- All product links now use detected locale for proper routing

src/app/not-found.tsx

@@ -1,33 +1,61 @@
 import { Metadata } from "next";
 import { getTranslations } from "next-intl/server";
 import { getProducts, getProductImage, getProductPrice } from "@/lib/saleor";
-import { getSaleorLocale, isValidLocale, DEFAULT_LOCALE } from "@/lib/i18n/locales";
-import type { Locale } from "@/lib/i18n/locales";
+import { 
+  getSaleorLocale, 
+  isValidLocale, 
+  DEFAULT_LOCALE, 
+  getLocaleFromPath,
+  LOCALE_COOKIE,
+  type Locale 
+} from "@/lib/i18n/locales";
 import type { Product } from "@/types/saleor";
 import Link from "next/link";
 import Image from "next/image";
 import { Star, ArrowRight } from "lucide-react";
 import { headers } from "next/headers";
+import { cookies } from "next/headers";
 
 export const metadata: Metadata = {
   title: "Page Not Found | ManoonOils",
   description: "Discover our bestselling natural oils for hair and skin care.",
 };
 
+function detectLocale(pathname: string, cookieLocale: string | undefined, acceptLanguage: string): Locale {
+  // First, check if URL has a locale prefix
+  const localeFromPath = getLocaleFromPath(pathname);
+  if (pathname.match(/^\/(sr|en|de|fr)/)) {
+    return localeFromPath as Locale;
+  }
+  
+  // Second, check cookie
+  if (cookieLocale && isValidLocale(cookieLocale)) {
+    return cookieLocale;
+  }
+  
+  // Third, check accept-language header
+  if (acceptLanguage.includes("en")) {
+    return "en";
+  }
+  
+  // Default to Serbian
+  return DEFAULT_LOCALE;
+}
+
 export default async function NotFoundPage() {
-  // Get locale from URL path
   const headersList = await headers();
   const pathname = headersList.get("x-invoke-path") || headersList.get("x-matched-path") || "/";
+  const acceptLanguage = headersList.get("accept-language") || "";
   
-  // Extract locale from path (e.g., /en/products → en, /sr/products → sr)
-  const pathSegments = pathname.split("/").filter(Boolean);
-  const potentialLocale = pathSegments[0];
-  const validLocale = isValidLocale(potentialLocale) ? potentialLocale : DEFAULT_LOCALE;
+  const cookieStore = await cookies();
+  const cookieLocale = cookieStore.get(LOCALE_COOKIE)?.value;
+  
+  const validLocale = detectLocale(pathname, cookieLocale, acceptLanguage);
   
   const t = await getTranslations({ locale: validLocale, namespace: "NotFound" });
   const productReviewT = await getTranslations({ locale: validLocale, namespace: "ProductReviews" });
   
-  const saleorLocale = getSaleorLocale(validLocale as Locale);
+  const saleorLocale = getSaleorLocale(validLocale);
   
   // Fetch products
   let products: Product[] = [];