Update sitemaps and improve language handling

- Updated last modification dates in static and tools sitemaps to 2026-04-01.
- Enhanced language switching in the Header component to ensure language resources are loaded before changing the language.
- Added language resource loading logic in i18n configuration to support dynamic loading of language files.
- Improved SEO route page to ensure correct language is set based on URL parameters.
- Adjusted global CSS for deferred sections to optimize rendering.
- Configured Nginx to enable Brotli compression for better performance.

frontend/nginx-frontend.conf

@@ -3,6 +3,10 @@ server {
     root /usr/share/nginx/html;
     index index.html;
 
+    gzip on;
+    gzip_types text/plain text/css application/json application/javascript text/xml application/xml text/javascript image/svg+xml;
+    gzip_min_length 1000;
+
     # SPA fallback
     location / {
         try_files $uri $uri/ /index.html;