fix: add nginx SPA fallback for BrowserRouter routing

Root cause: Docker container was 4 days old and nginx had no
try_files fallback for SPA routes like /details.

Changes:
- Add nginx.conf with try_files $uri $uri/ /index.html
- Update Dockerfile to copy nginx config
- Add production browser QA script

Production verified:
- https://arhipovdan.ru/ shows full-screen 3D demo
- https://arhipovdan.ru/details shows detailed page

Dockerfile

@@ -7,5 +7,6 @@ RUN npm run build
 
 FROM nginx:alpine AS runtime
 COPY --from=build /app/dist /usr/share/nginx/html
+COPY nginx.conf /etc/nginx/conf.d/default.conf
 EXPOSE 80
 CMD ["nginx", "-g", "daemon off;"]