Restore multilingual support: / for sr, /en for en with browser detection

src/i18n/routing.ts

@@ -1,6 +1,7 @@
 import { defineRouting } from 'next-intl/routing';
 
 export const routing = defineRouting({
-  locales: ['sr'],
-  defaultLocale: 'sr'
+  locales: ['sr', 'en'],
+  defaultLocale: 'sr',
+  localePrefix: 'as-needed'
 });