add example in docker-compose, clarify README, add clearer validation, longer timeouts for websocket connections

frontend/docker-entrypoint.sh

@@ -1,7 +1,8 @@
 #!/bin/sh
+# Alpine-based image uses /bin/sh (busybox ash), not bash
 set -e
 
-# Set default backend URL if not provided
+# Set default backend URL if not provided (host:port format, no protocol)
 export BACKEND_URL="${BACKEND_URL:-backend:8000}"
 
 echo "Configuring nginx with BACKEND_URL: ${BACKEND_URL}"
@@ -11,7 +12,11 @@ echo "Configuring nginx with BACKEND_URL: ${BACKEND_URL}"
 envsubst '${BACKEND_URL}' < /etc/nginx/nginx.conf.template > /etc/nginx/nginx.conf
 
 # Validate the generated nginx configuration before starting
-nginx -t -c /etc/nginx/nginx.conf
+echo "Validating nginx configuration..."
+if ! nginx -t -c /etc/nginx/nginx.conf; then
+    echo "ERROR: nginx configuration validation failed" >&2
+    exit 1
+fi
 
 # Execute the main command (nginx)
-exec "$@"
+exec "$@"