docs: add nginx gzip configuration for JSON compression

Activity index shards compress ~90% with gzip (130 KB → 14 KB).
The default nginx.conf has gzip on but gzip_types commented out,
so JSON was served uncompressed.

docs/deployment/vps.md

@@ -293,6 +293,26 @@ ln -s /etc/nginx/sites-available/bincio /etc/nginx/sites-enabled/
 nginx -t && systemctl reload nginx
 ```
 
+### Enable gzip compression
+
+The default `nginx.conf` has gzip on but `gzip_types` commented out, so only
+HTML is compressed. Activity index shards are JSON and compress ~90% — enable
+the full list:
+
+```bash
+# In /etc/nginx/nginx.conf, uncomment the gzip block:
+gzip_vary on;
+gzip_proxied any;
+gzip_comp_level 6;
+gzip_buffers 16 8k;
+gzip_http_version 1.1;
+gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;
+```
+
+```bash
+nginx -t && systemctl reload nginx
+```
+
 You can verify the site is served correctly by hitting the IP directly:
 `http://<your-vps-ip>/` — you should see the bincio activity feed, not the nginx welcome page.