Raise upload limit from 50 MB to 500 MB

Both limits that gate uploads are bumped in tandem so they don't conflict:
- settings.defaults.js maxUploadSize: 50 MB → 500 MB (app-level check)
- nginx.conf.template client_max_body_size: 50m → 500m (proxy body limit)

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

server-ce/nginx/nginx.conf.template

@@ -46,7 +46,7 @@ http {
 	gzip_disable "msie6";
 	gzip_proxied any; # allow upstream server to compress.
 
-	client_max_body_size 50m;
+	client_max_body_size 500m;
 
 	# gzip_vary on;
 	# gzip_proxied any;