SEO: add crawlable language navigation links for Google indexing

- Add sr-only CSS class for screen-reader/crawler-visible elements
- Add hidden <nav> with real <a> links to all 6 language versions in template.html
- Googlebot can now discover /de/, /fr/, /es/, /pt-BR/, /ru/ via HTML links
- No visual changes - existing <select> dropdown remains the user-facing switcher
- Rebuild all www/ output with updated CSS hash

website/www/de/index.html

@@ -6,9 +6,9 @@
     <title>KoalaSync | Netflix, YouTube & jedes Video mit Freunden synchronisieren</title>
     <meta name="description" content="Schaue Netflix, YouTube, Twitch und jedes HTML5-Video synchron mit Freunden. Kostenlose, quelloffene Browser-Erweiterung. Keine Anmeldung erforderlich.">
     
-    <link rel="preload" href="../style.e78fc9fc.min.css" as="style">
+    <link rel="preload" href="../style.adcf0bc0.min.css" as="style">
     <link rel="preload" as="image" href="../assets/LookDownKoala.webp" imagesrcset="../assets/LookDownKoala-1x.webp 90w, ../assets/LookDownKoala.webp 205w" imagesizes="90px" fetchpriority="high">
-    <link rel="stylesheet" href="../style.e78fc9fc.min.css">
+    <link rel="stylesheet" href="../style.adcf0bc0.min.css">
     <link rel="icon" type="image/webp" href="../assets/NewLogoIcon_64.webp">
     <link rel="canonical" href="https://sync.koalastuff.net/de/">
     <link rel="alternate" hreflang="en" href="https://sync.koalastuff.net/">
@@ -204,6 +204,14 @@
                     </select>
                     <svg xmlns="http://www.w3.org/2000/svg" fill="none" stroke="currentColor" stroke-linecap="round" stroke-linejoin="round" stroke-width="2" aria-hidden="true" class="chevron-icon" viewBox="0 0 24 24"><path d="m6 9 6 6 6-6"/></svg>
                 </div>
+                <nav class="sr-only" aria-label="Language alternatives">
+                    <a href="https://sync.koalastuff.net/" hreflang="en">English</a>
+                    <a href="https://sync.koalastuff.net/de/" hreflang="de">Deutsch</a>
+                    <a href="https://sync.koalastuff.net/fr/" hreflang="fr">Français</a>
+                    <a href="https://sync.koalastuff.net/es/" hreflang="es">Español</a>
+                    <a href="https://sync.koalastuff.net/pt-BR/" hreflang="pt-br">Português (Brasil)</a>
+                    <a href="https://sync.koalastuff.net/ru/" hreflang="ru">Русский</a>
+                </nav>
             </div>
         </div>
     </nav>