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/template.html

@@ -204,6 +204,14 @@
                     </select>
                     <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true" class="chevron-icon"><polyline points="6 9 12 15 18 9"/></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>