feat: add hreflang tags and international sitemap for SEO

- Added hreflang alternates to root layout for all locales (sr, en, de, fr)
- Added hreflang alternates to [locale] layout for all locales
- Updated sitemap to include all locale variants for every page
- Google will now properly index all language versions

src/app/[locale]/layout.tsx

@@ -1,11 +1,36 @@
+import { Metadata } from "next";
 import { NextIntlClientProvider } from "next-intl";
 import { getMessages, setRequestLocale } from "next-intl/server";
 import { routing } from "@/i18n/routing";
 
+const baseUrl = process.env.NEXT_PUBLIC_SITE_URL || "https://dev.manoonoils.com";
+
 export function generateStaticParams() {
   return routing.locales.map((locale) => ({ locale }));
 }
 
+export async function generateMetadata({
+  params,
+}: {
+  params: Promise<{ locale: string }>;
+}): Promise<Metadata> {
+  const { locale } = await params;
+  const localePrefix = locale === "sr" ? "" : `/${locale}`;
+
+  const languages: Record<string, string> = {};
+  for (const loc of routing.locales) {
+    const prefix = loc === "sr" ? "" : `/${loc}`;
+    languages[loc] = `${baseUrl}${prefix}`;
+  }
+
+  return {
+    alternates: {
+      canonical: `${baseUrl}${localePrefix}`,
+      languages,
+    },
+  };
+}
+
 export default async function LocaleLayout({
   children,
   params,
@@ -22,4 +47,4 @@ export default async function LocaleLayout({
       {children}
     </NextIntlClientProvider>
   );
-}
+}