fix: add public/favicon.ico and location = /favicon.ico fallback to eliminate 504/404 errors

nginx.conf

@@ -13,6 +13,13 @@ server {
     gzip on;
     gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript;
 
+    # Favicon handling
+    location = /favicon.ico {
+        try_files $uri /favicon.svg =200;
+        access_log off;
+        log_not_found off;
+    }
+
     # Priority prefix location for uploads - proxies to Express backend container
     location ^~ /uploads/ {
         proxy_pass http://backend:3005/uploads/;