fix: implement Flush on trackingResponseWriter

Allows the trackingResponseWriter to properly proxy flush
requests to the underlying http.Flusher. This ensures
compatibility with streaming responses.

cmd/api-response.go

@@ -1060,6 +1060,12 @@ func (w *trackingResponseWriter) Write(b []byte) (int, error) {
 	return w.ResponseWriter.Write(b)
 }
 
+func (w *trackingResponseWriter) Flush() {
+	if f, ok := w.ResponseWriter.(http.Flusher); ok {
+		f.Flush()
+	}
+}
+
 func (w *trackingResponseWriter) Unwrap() http.ResponseWriter {
 	return w.ResponseWriter
 }