nginx: /shared/ edge cache 5 min (was 1 h) so navbar/footer changes reach every site quickly

ddiff --git a/deploy/nginx/openvibe.network.conf b/deploy/nginx/openvibe.network.conf
iindex 020647ba..1f620a89 100644
---- a/deploy/nginx/openvibe.network.conf
++++ b/deploy/nginx/openvibe.network.conf
@@@ -69,8 +69,10 @@ server {
          proxy_pass http://127.0.0.1:4000;
          proxy_http_version 1.1;
          proxy_set_header Host $host;
--        proxy_cache_valid 200 1h;
--        add_header Cache-Control "public, max-age=3600";
++        # Shared browser modules are loaded by every OpenVibe site from here. Five minutes at the
++        # edge: a navbar/footer change reaches the whole network within minutes instead of an hour.
++        add_header Cache-Control "public, max-age=300, stale-while-revalidate=60";
++        add_header Access-Control-Allow-Origin "*";
      }
  
      # ── API (moderate rate limit) ───────────────────────────