Redesign language switcher with circular flag icons

Desktop dropdown and mobile modal now show circular country flags (flag-icons) with clean language names and an active-language highlight, driven by the page lang via main.js.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

main.js

@@ -122,10 +122,12 @@ document.addEventListener('DOMContentLoaded', function() {
                 pathWithoutLang = path;
             }
 
+            const docLang = (document.documentElement.getAttribute('lang') || 'en').toLowerCase();
             document.querySelectorAll('a[data-lang]').forEach(link => {
                 const targetLang = link.getAttribute('data-lang');
                 const newUrl = `/${targetLang}${pathWithoutLang}`;
                 link.setAttribute('href', newUrl.replace(/\/{2,}/g, '/'));
+                link.classList.toggle('is-current', targetLang === docLang);
             });
 
             const desktopSelectors = document.querySelectorAll('.header-right-wrapper .language-selector');