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

frontend/nginx.conf

@@ -0,0 +1,57 @@
+worker_processes auto;
+
+events {
+    worker_connections 1024;
+}
+
+http {
+    include       /etc/nginx/mime.types;
+    default_type  application/octet-stream;
+    sendfile      on;
+    tcp_nopush    on;
+
+    gzip on;
+    gzip_vary on;
+    gzip_proxied any;
+    gzip_comp_level 6;
+    gzip_min_length 1000;
+    gzip_types
+        text/plain
+        text/css
+        text/javascript
+        application/javascript
+        application/json
+        application/xml
+        image/svg+xml
+        font/woff2;
+
+    server {
+        listen 80;
+        root /usr/share/nginx/html;
+        index index.html;
+
+        # Long-lived cache for hashed assets (JS/CSS chunks)
+        location ~* \.(js|css)$ {
+            add_header Cache-Control "public, max-age=31536000, immutable";
+            try_files $uri =404;
+        }
+
+        # Cache static assets
+        location ~* \.(svg|ico|png|jpg|jpeg|woff2|woff)$ {
+            add_header Cache-Control "public, max-age=604800";
+            try_files $uri =404;
+        }
+
+        # env.js must never be cached (runtime config)
+        location = /env.js {
+            add_header Cache-Control "no-store";
+            try_files $uri =404;
+        }
+
+        # SPA fallback
+        location / {
+            try_files $uri $uri/ /index.html;
+            add_header Cache-Control "no-cache";
+        }
+    }
+}