fix: set client_max_body_size 0 at http level in demo nginx

Location-level override wasn't sufficient. Setting at http block
disables the body size limit globally for the demo.

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

neode-ui/docker/nginx-demo.conf

@@ -14,6 +14,9 @@ http {
     gzip on;
     gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;
 
+    # Allow large uploads globally (filebrowser, etc.)
+    client_max_body_size 0;
+
     server {
         listen 80 default_server;
         server_name _;