feat: enable browser language detection for locale routing

- Root / now uses next-intl locale detection to redirect based on
  Accept-Language header (English browser → /en, Serbian → /sr, etc.)
- Old Serbian URLs (/products, /about, etc.) still redirect to /sr/* with 301
- English URLs (/en/*) remain unchanged

middleware.ts

@@ -3,37 +3,43 @@ import { NextResponse } from "next/server";
 import type { NextRequest } from "next/server";
 import { routing } from "./src/i18n/routing";
 
-const oldSerbianPaths = ["", "products", "about", "contact", "checkout"];
-
 export default function middleware(request: NextRequest) {
   const pathname = request.nextUrl.pathname;
 
-  const isOldSerbianPath = oldSerbianPaths.some((path) => {
-    if (path === "") {
-      return pathname === "/";
-    }
-    return pathname === `/${path}` || pathname.startsWith(`/${path}/`);
-  });
-
   const hasLocalePrefix = routing.locales.some(
     (locale) => pathname === `/${locale}` || pathname.startsWith(`/${locale}/`)
   );
 
-  if (isOldSerbianPath && !hasLocalePrefix) {
-    const newPathname = pathname === "/"
-      ? "/sr"
-      : `/sr${pathname}`;
+  if (hasLocalePrefix) {
+    const intlMiddleware = createMiddleware({
+      ...routing,
+    });
+    return intlMiddleware(request);
+  }
 
+  if (pathname === "/" || pathname === "") {
+    const intlMiddleware = createMiddleware({
+      ...routing,
+      localeDetection: true,
+    });
+    return intlMiddleware(request);
+  }
+
+  const oldSerbianPaths = ["products", "about", "contact", "checkout"];
+  const isOldSerbianPath = oldSerbianPaths.some(
+    (path) => pathname === `/${path}` || pathname.startsWith(`/${path}/`)
+  );
+
+  if (isOldSerbianPath) {
+    const newPathname = `/sr${pathname}`;
     const url = request.nextUrl.clone();
     url.pathname = newPathname;
-    
     return NextResponse.redirect(url, 301);
   }
 
   const intlMiddleware = createMiddleware({
     ...routing,
   });
-
   return intlMiddleware(request);
 }