feat: add i18n with English (default) and PT-BR (/pt-br)

- Translate index.html to English as default language
- Copy PT-BR version to index.pt-br.html
- Add hreflang tags for SEO in both versions
- Add language selector in navbar (EN ↔ PT-BR)
- Add nginx.conf with Content-Language headers and /pt-br routing
- Update Dockerfile to process and serve both HTML files

Dockerfile

@@ -3,7 +3,14 @@ FROM nginx:alpine
 ARG APP_URL=https://app.batida.io
 
 COPY index.html /tmp/index.html
-RUN sed -i "s|{{APP_URL}}|${APP_URL}|g" /tmp/index.html
-RUN mv /tmp/index.html /usr/share/nginx/html/index.html
+COPY index.pt-br.html /tmp/index.pt-br.html
+
+RUN sed -i "s|{{APP_URL}}|${APP_URL}|g" /tmp/index.html && \
+    sed -i "s|{{APP_URL}}|${APP_URL}|g" /tmp/index.pt-br.html && \
+    mkdir -p /usr/share/nginx/html/pt-br && \
+    mv /tmp/index.html /usr/share/nginx/html/index.html && \
+    mv /tmp/index.pt-br.html /usr/share/nginx/html/pt-br/index.html
+
+COPY nginx.conf /etc/nginx/conf.d/default.conf
 
 EXPOSE 80