feat(website): technical SEO and UI/UX accessibility improvements

- Add LCP image preload for hero mascot
- Add HowTo structured data schema (3-step install guide)
- Update SoftwareApplication schema with screenshot + image fields
- Add glassmorphic :focus-visible outlines for keyboard accessibility
- Add content-visibility: auto to heavy offscreen sections for INP
- Expand lang-init.js auto-redirect to all 6 supported languages
- Remove impressum/datenschutz from sitemap.xml (noindex conflict)

website/lang-init.js

@@ -1,22 +1,30 @@
 (function() {
     var html = document.documentElement;
     var path = window.location.pathname;
-    
+
+    // Mapping of browser language codes to KoalaSync locale directories
+    var langMap = {
+        'de': 'de',
+        'fr': 'fr',
+        'es': 'es',
+        'pt': 'pt-BR',
+        'ru': 'ru'
+    };
+
     // Check if we are on the root index page (either "/" or "/index.html" at the root)
     var isRootIndex = path === '/' || path === '/index.html' || path === '';
-    
+
     if (isRootIndex) {
         var savedLang = localStorage.getItem('koala_lang');
-        var browserLang = navigator.language.startsWith('de') ? 'de' : 'en';
-        var preferredLang = savedLang || browserLang;
-        
-        if (preferredLang === 'de') {
-            // Redirect to German version
-            window.location.replace('de/');
+        var browserLang = navigator.language.split('-')[0];
+        var preferredLang = savedLang || langMap[browserLang] || 'en';
+
+        if (preferredLang !== 'en') {
+            window.location.replace(preferredLang + '/');
             return;
         }
     }
-    
+
     var htmlClasses = html.className.split(' ');
     var activeLang = null;
     var hasStaticLang = false;
@@ -28,38 +36,38 @@
             break;
         }
     }
-    
+
     if (hasStaticLang) {
         localStorage.setItem('koala_lang', activeLang);
     } else {
         var savedLang = localStorage.getItem('koala_lang');
-        var browserLang = navigator.language.startsWith('de') ? 'de' : 'en';
-        activeLang = savedLang || browserLang;
-        
+        var browserLang = navigator.language.split('-')[0];
+        activeLang = savedLang || langMap[browserLang] || 'en';
+
         // Dynamic utility pages currently only support English and German markup.
-        // Fallback to English for any other language preference (e.g. fr, es) to avoid bilingual text duplication.
+        // Fallback to English for any other language to avoid bilingual text duplication.
         if (activeLang !== 'de') {
             activeLang = 'en';
         }
-        
+
         html.classList.add('lang-' + activeLang);
         html.lang = activeLang;
     }
-    
+
     // Update titles dynamically based on page
     var isIndex = path === '/' || path.endsWith('index.html') || path.split('/').pop() === '';
     var isJoin = path.includes('join');
-    
+
     if (isIndex) {
-        var titles = { 
-            en: 'KoalaSync | Real-time Video Synchronization for Friends', 
-            de: 'KoalaSync | Echtzeit-Video-Synchronisation für Freunde' 
+        var titles = {
+            en: 'KoalaSync | Real-time Video Synchronization for Friends',
+            de: 'KoalaSync | Echtzeit-Video-Synchronisation für Freunde'
         };
         document.title = titles[activeLang] || titles.en;
     } else if (isJoin) {
-        var titles = { 
-            en: 'Join Room | KoalaSync', 
-            de: 'Raum beitreten | KoalaSync' 
+        var titles = {
+            en: 'Join Room | KoalaSync',
+            de: 'Raum beitreten | KoalaSync'
         };
         document.title = titles[activeLang] || titles.en;
     }