Perf: add nginx gzip compression and cache headers

- gzip level 6 for JS, CSS, JSON, SVG, fonts
- immutable cache (1yr) for hashed JS/CSS assets
- 7-day cache for static assets (SVG, fonts, images)
- no-store for env.js (runtime config must be fresh)
- no-cache for HTML (SPA index)

Reduces JS transfer from ~460KB to ~115KB gzip.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/Dockerfile

@@ -9,6 +9,7 @@ RUN npm run build
 # Stage 2: serve the static files
 FROM nginx:alpine
 COPY --from=build /app/dist /usr/share/nginx/html
+COPY nginx.conf /etc/nginx/nginx.conf
 COPY entrypoint.sh /entrypoint.sh
 RUN chmod +x /entrypoint.sh
 EXPOSE 80